Router device and datagram transfer method for data communication network system

ABSTRACT

A router device realizing a datagram transfer method for improving the datagram transfer efficiency by ascertaining the transfer target and/or the requested quality of service without referring to the datagram content. The router device has network interfaces connected with networks including at least one virtual connection oriented network, a table for registering a correspondence between a virtual connection identifier and a transfer target network interface and/or a quality of service, a connection identifier analysis unit for determining a transfer target network interface and/or a quality of service for a datagram entered from one virtual connection, by referring to the table according to a virtual connection identifier of that one virtual connection. The datagram can be transferred to the determined transfer target network interface, while applying a priority control for datagrams to be transferred by the router device according to the determined quality of service.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a router device for connecting avirtual connection network with another virtual connection network ornon-virtual connection network, and a datagram transfer method using arouter device in a data communication network system.

2. Description of the Background Art

A router device is used for connecting LANs, and transferring datagramfrom one LAN to another LAN. Datagram contains communication data aswell as source and final destination network layer addresses (such as IPaddresses in a case of IP), and the router device determines an outputinterface and a next transfer node (a router device or a hostfunctioning as a communication terminal) for the datagram according tothese address information.

Here, a datagram transfer scheme in a conventional router device will bedescribed with reference to FIG. 1, for an exemplary case of a routerdevice connected with Ethernet which is a non-virtual connectionoriented LAN. When an Ethernet frame (datalink frame) is received from aLAN, a reception unit 911 changes the received datalink frame into adatagram suitable for handling at the network layer. Then, a datagramanalysis unit 921 determines an output interface and a network layeraddress of a next transfer node (a host or a router device) from thefinal destination address of that datagram, and gives that datagram to adatagram processing unit 922 of the determined output interface via atransfer unit 930. The datagram processing unit 922 which received thedatagram then carries out the network layer processing (a processing toreduce TTL (Time To Live), a checksum calculation, an optionalprocessing, etc. in a case of IP). Finally, a transmission unit 913determines an Ethernet address (datalink layer address) from the networklayer address of the next transfer node, constructs an Ethernet framefrom that address and the datagram, and outputs the constructed Ethernetframe to the LAN.

The datagram transfer is carried out similarly in a case of ATM which isa virtual connection oriented LAN. First, when an ATM cell is receivedfrom a LAN, the received ATM cell is changed into an AAL (ATM adaptationLayer) frame (datalink frame), and this AAL frame is changed into adatagram suitable for handling at the network layer. Then, an outputinterface and a network layer address of a next transfer node isdetermined from the final destination address of that datagram, and thenetwork layer processing is carried out. Finally, at the transmissionunit 913, a virtual connection identifier of a virtual connection fortransferring the datagram is determined from the network layer addressof the next transfer node, an ATM cell is constructed from thatidentifier and the datagram, and the constructed ATM cell is outputtedto the LAN.

Now, regardless of whether it is a router device connected with thevirtual connection oriented LAN or a router device connected with thenon-virtual connection oriented LAN, at a time of transferring datagram,an output target is determined by referring to datagram content(including a header information such as a source address, a destinationaddress, and a type of service, and an upper layer information such as aport address in a case of IP) at a datagram analysis unit. For thisreason, a considerable transfer processing time is taken by the datagramanalysis unit, and consequently it has been impossible to realize a highspeed transfer of datagram.

Moreover, when the requested quality of service is different fordifferent datagrams to be transferred, it is preferable to carry out theprocessing which accounts for the requested quality of service fordifferent datagrams rather than just processing datagrams according toan order of their arrivals. To this end, as shown in FIG. 2, it ispossible to provide a function called scheduler 961, which controls anorder by which datagrams are to be given to a next function not justaccording to their arrival order but also by accounting for theirrequested quality of service.

However, an information concerning the quality of service requested toeach datagram is to be obtained by referring to datagram content, sothat as shown in FIG. 2, it has been necessary to carry out a prioritycontrol processing (scheduling) at the scheduler 961 only after theprocessing at the datagram analysis unit 921 is applied, according tothe result of this processing at the datagram analysis unit 921. Thisscheduling is effective in a case of output processing datagrams in anorder of their requested quality of service when a transmissioninterface to a next hop node does not have a sufficient capacity.

But, in a case where the analysis processing power of the datagramanalysis unit 921 itself is not sufficient, despite of the fact that aprocessing wait time at the datagram analysis unit 921 can be a problemfrom a viewpoint of an overall performance, the scheduling accountingfor the quality of service cannot be carried out at this point becausethe priority level information is not yet available at this point, andconsequently it has been necessary for the scheduler 961 to carry outthe processing in the arrival order.

Thus in a conventional router device, the transfer target cannot bedetermined and the quality of service cannot be ascertained until thedatagram content is referred.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a routerdevice and a datagram transfer method capable of improving the datagramtransfer efficiency by ascertaining the transfer target withoutreferring to the datagram content.

It is another object of the present invention to provide a router deviceand a datagram transfer method capable of improving the datagramtransfer efficiency by ascertaining the requested quality of service forthe datagram without referring to the datagram content, and carrying outthe transfer accounting for the requested quality of service for thedatagram more effectively.

According to one aspect of the present invention there is provided arouter device for transferring datagrams among networks, comprising:network interfaces connected with networks including at least onevirtual connection oriented network; table means for registering acorrespondence between a virtual connection identifier and a transfertarget network interface; connection identifier analysis means fordetermining a transfer target network interface for a datagram enteredfrom one virtual connection, by referring to the table means accordingto a virtual connection identifier of said one virtual connection; andtransfer means for transferring the datagram to the transfer targetnetwork interface determined by the connection identifier analysismeans.

According to another aspect of the present invention there is provided arouter device for transferring datagrams among networks, comprising: atleast one network interface connected with at least one virtualconnection oriented network; tables means for registering acorrespondence between a virtual connection identifier and an outputvirtual connection identifier; connection identifier analysis means fordetermining an output virtual connection identifier for a datagramentered from one virtual connection, by referring to the table meansaccording to a virtual connection identifier of said one virtualconnection; and transfer means for transferring the datagram such thatthe datagram is outputted to a virtual connection having the outputvirtual connection identifier determined by the connection identifieranalysis means.

According to another aspect of the present invention there is provided arouter device for transferring datagrams among networks, comprising: atleast one network interface connected with at least one virtualconnection oriented network; table means for registering acorrespondence between a virtual connection identifier and a quality ofservice; connection identifier analysis means for determining a qualityof service for a datagram entered from one virtual connection, byreferring to the table means according to a virtual connectionidentifier of said one virtual connection; scheduler means for applyinga priority control for datagrams to be transferred by the router deviceaccording to the quality of service determined by the connectionidentifier analysis means; and transfer means for transferring thedatagram to which the priority control is applied by the schedulermeans.

According to another aspect of the present invention there is provided arouter device for transferring ATM cells from an ATM network,comprising: network interfaces connected with networks including atleast one ATM network, each network interface connected with said atleast one ATM network including reception means for receiving ATM cellstransmitted from an ATM network and assembling an AAL frame from thereceived ATM cells, and transmission means for forming ATM cells from anAAL frame and transmitting the formed ATM cells to an ATM network; tablemeans for registering a correspondence between a virtual connectionidentifier and a transfer target network interface; connectionidentifier analysis means for determining a transfer target networkinterface for an AAL frame assembled from ATM cells entered from onevirtual connection, by referring to the table means according to avirtual connection identifier of said one virtual connection; processingmeans for determining a transfer target network interface for the AALframe by assembling datagram from the AAL frame and analyzing theassembled datagram, when the table means does not register the transfertarget network interface in correspondence to the virtual connectionidentifier of said one virtual connection; and transfer means fortransferring the AAL frame to the transfer target network interfacedetermined by one of the connection identifier analysis means and theprocessing means.

According to another aspect of the present invention there is provided arouter device for transferring AAL frames from an ATM network throughnetwork interfaces connected with networks including at least one ATMnetwork, each network interface connected with said at least one ATMnetwork including reception means for receiving ATM cells transmittedfrom an ATM network and assembling an AAL frame from the received ATMcells, and transmission means for forming ATM cells from an AAL frameand transmitting the formed ATM cells to an ATM network, the routerdevice comprising: table means for registering a correspondence betweena virtual connection identifier and a transfer target network interface;connection identifier analysis means for determining a transfer targetnetwork interface for an AAL frame assembled from ATM cells entered fromone virtual connection, by referring to the table means according to avirtual connection identifier of said one virtual connection; processingmeans for determining a transfer target network interface for the AALframe by assembling datagram from the AAL frame and analyzing theassembled datagram, when the table means does not register the transfertarget network interface in correspondence to the virtual connectionidentifier of said one virtual connection; and transfer means fortransferring the AAL frame to the transfer target network interfacedetermined by one of the connection identifier analysis means and theprocessing means.

According to another aspect of the present invention there is providedan ATM network interface card device for interfacing an ATM network anda bus connecting other network interfaces connected with other networks,the ATM network interface card device comprising: reception means forreceiving ATM cells transmitted from the ATM network and assembling anAAL frame from the received ATM cells; table means for registering acorrespondence between a virtual connection identifier and a transfertarget network interface; connection identifier analysis means fordetermining a transfer target network interface for one AAL frameassembled from ATM cells entered from one virtual connection, byreferring to the table means according to a virtual connectionidentifier of said one virtual connection; and transfer means fortransferring said one AAL frame through the bus to the transfer targetnetwork interface determined by the connection identifier analysismeans.

According to another aspect of the present invention there is provided arouter device for transferring ATM cells from an ATM network,comprising: at least one network interface connected with at least oneATM network, each network interface connected with said at least one ATMnetwork including reception means for receiving ATM cells transmittedfrom an ATM network and assembling an AAL frame from the received ATMcells, and transmission means for forming ATM cells from an AAL frameand transmitting the formed ATM cells to an ATM network; table means forregistering a correspondence between a virtual connection identifier andan output virtual connection identifier; connection identifier analysismeans for determining an output virtual connection identifier for an AALframe assembled from ATM cells entered from one virtual connection, byreferring to the table means according to a virtual connectionidentifier of said one virtual connection; processing means fordetermining an output virtual connection identifier for the AAL frame byassembling datagram from the AAL frame and analyzing the assembleddatagram, when the table means does not register the output virtualconnection identifier in correspondence to the virtual connectionidentifier of said one virtual connection; and transfer means fortransferring the AAL frame such that the AAL frame is outputted to avirtual connection having the output virtual connection identifierdetermined by one of the connection identifier analysis means and theprocessing means.

According to another aspect of the present invention there is provided arouter device for transferring datagrams among networks, comprising: atleast one network interface connected with at least one virtualconnection oriented network; table means for registering acorrespondence between a virtual connection identifier and a protocoltype information indicating a type and/or a version of a protocol;connection identifier analysis means for determining a protocol typeinformation for a datagram entered from one virtual connection, byreferring to the table means according to a virtual connectionidentifier of said one virtual connection; datagram analysis means fordetermining a transfer target network interface/next hop network layeraddress for the datagram according to a datagram content of thedatagram, the datagram analysis means having a plurality of processorsin correspondence to different protocols, and the datagram is enteredinto one of said plurality of processors which corresponds to a protocolof a type and/or a version indicated by the protocol type informationdetermined by the connection identifier analysis means; and transfermeans for transferring the datagram to the transfer target networkinterface/next hop network layer address determined by the datagramanalysis means.

According to another aspect of the present invention there is provided amethod for transferring datagrams among networks, using a router devicehaving network interfaces connected with networks including at least onevirtual connection oriented network, the method comprising the steps of:registering a correspondence between a virtual connection identifier anda transfer target network interface in a table provided at the routerdevice; determining a transfer target network interface for a datagramentered from the virtual connection at the router device, by referringto the table according to a virtual connection identifier of said onevirtual connection; and transferring the datagram to the transfer targetnetwork interface determined by the determining step.

According to another aspect of the present invention there is provided amethod for transferring datagrams among networks, using a router devicehaving at least one network interface connected with at least onevirtual connection oriented network, the method comprising the steps of:registering a correspondence between a virtual connection identifier andan output virtual connection identifier in a table provided at therouter device; determining an output virtual connection identifier for adatagram entered from one virtual connection, by referring to the tableaccording to a virtual connection identifier of said one virtualconnection; and transferring the datagram such that the datagram isoutputted to a virtual connection having the output virtual connectionidentifier determined by the determining step.

According to another aspect of the present invention there is provided amethod for transferring datagrams among networks, using a router devicehaving at least one network interface connected with at least onevirtual connection oriented network, the method comprising the steps of:registering a correspondence between a virtual connection identifier anda quality of service in a table provided at the router device;determining a quality of service for a datagram entered from one virtualconnection at the router device, by referring to the table according toa virtual connection identifier of said one virtual connection; applyinga priority control for datagrams to be transferred by the router deviceaccording to the quality of service determined by the determining step;and transferring the datagram to which the priority control is appliedby the applying step.

According to another aspect of the present invention there is provided amethod for transferring ATM cells from an ATM network, using a routerdevice having network interfaces connected with networks including atleast one ATM network, each network interface connected with said atleast one ATM network including reception means for receiving ATM cellstransmitted from an ATM network and assembling an AAL frame from thereceived ATM cells, and transmission means for forming ATM cells from anAAL frame and transmitting the formed ATM cells to an ATM network, themethod comprising the steps of: registering a correspondence between avirtual connection identifier and a transfer target network interface ina table provided at the router device; determining a transfer targetnetwork interface for an AAL frame assembled from ATM cells entered fromone virtual connection, by referring to the table according to a virtualconnection identifier of said one virtual connection; processing the AALframe to determine a transfer target network interface for the AAL frameby assembling datagram from the AAL frame and analyzing the assembleddatagram, when the table does not register the transfer target networkinterface in correspondence to the virtual connection identifier of saidone virtual connection; and transferring the AAL frame to the transfertarget network interface determined by one of the determining step andthe processing step.

According to another aspect of the present invention there is provided amethod for transferring AAL frames from an ATM network, using a routerdevice having network interfaces connected with networks including atleast one ATM network, each network interface connected with said atleast one ATM network including reception means for receiving ATM cellstransmitted from an ATM network and assembling an AAL frame from thereceived ATM cells, and transmission means for forming ATM cells from anAAL frame and transmitting the formed ATM cells to an ATM network, themethod comprising the steps of: registering a correspondence between avirtual connection identifier and a transfer target network interface ina table provided at the router device; determining a transfer targetnetwork interface for an AAL frame assembled from ATM cells entered fromone virtual connection, by referring to the table according to a virtualconnection identifier of said one virtual connection; processing the AALframe to determine a transfer target network interface for the AAL frameby assembling datagram from the AAL frame and analyzing the assembleddatagram, when the table does not register the transfer target networkinterface in correspondence to the virtual connection identifier of saidone virtual connection; and transferring the AAL frame to the transfertarget network interface determined by one of the determining step andthe processing step.

According to another aspect of the present invention there is provided amethod for interfacing an ATM network and a bus connecting other networkinterfaces connected with other networks, the method comprising thesteps of: receiving ATM cells transmitted from the ATM network andassembling an AAL frame from the received ATM cells; registering acorrespondence between a virtual connection identifier and a transfertarget network interface in a table; determining a transfer targetnetwork interface for one AAL frame assembled from ATM cells enteredfrom one virtual connection, by referring to the table according to avirtual connection identifier of said one virtual connection; andtransferring said one AAL frame through the bus to the the transfertarget network interface determined by the determining step.

According to another aspect of the present invention there is provided amethod for transferring ATM cells from an ATM network, using a routerdevice having at least one network interface connected with at least oneATM network, each network interface connected with said at least one ATMnetwork including reception means for receiving ATM cells transmittedfrom an ATM network and assembling an AAL frame from the received ATMcells, and transmission means for forming ATM cells from an AAL frameand transmitting the formed ATM cells to an ATM network, the methodcomprising the steps of: registering a correspondence between a virtualconnection identifier and an output virtual connection identifier in atable provided at the router device; determining an output virtualconnection identifier for an AAL frame assembled from ATM cells enteredfrom one virtual connection, by referring to the table according to avirtual connection identifier of said one virtual connection; processingthe AAL frame to determine an output virtual connection identifier forthe AAL frame by assembling datagram from the AAL frame and analyzingthe assembled datagram, when the table does not register the outputvirtual connection identifier in correspondence to the virtualconnection identifier of said one virtual connection; and transferringthe AAL frame such that the AAL frame is outputted to a virtualconnection having the output virtual connection identifier determined byone of the determining step and the processing step.

According to another aspect of the present invention there is provided amethod for transferring datagrams among networks, using a router devicehaving at least one network interface connected with at least onevirtual connection oriented network, the method comprising the steps of:registering a correspondence between a virtual connection identifier anda protocol type information indicating a type and/or a version of aprotocol in a table provided at the router device; determining aprotocol type information for a datagram entered from one virtualconnection, by referring to the table according to a virtual connectionidentifier of said one virtual connection; determining a transfer targetnetwork interface/next hop network layer address for the datagramaccording to a datagram content of the datagram, wherein a plurality ofprocessors are provided at the router device in correspondence todifferent protocols, and the datagram is entered into one of saidplurality of processors which corresponds to a protocol of a type and/ora version indicated by the protocol type information determined by thedetermining step; and transferring the datagram to the determinedtransfer target network interface/next hop network layer address.

According to another aspect of the present invention there is provided adata communication network system, comprising: networks including atleast one virtual connection oriented network; a transmission nodeprovided in each network for transmitting datagrams such that datagramsdestined to an identical destination are transmitted through specificvirtual connection; and a router device for connecting at least two ofthe networks, the router device including: network interfaces connectedwith said at least two of the networks; table means for registering acorrespondence between a virtual connection identifier and a transfertarget network interface; connection identifier analysis means fordetermining a transfer target network interface for a datagram enteredfrom one virtual connection, by referring to the table means accordingto a virtual connection identifier of said one virtual connection; andtransfer means for transferring the datagram to the transfer targetnetwork interface determined by the connection identifier analysismeans.

According to another aspect of the present invention there is provided adata communication network system, comprising: networks including atleast one virtual connection oriented network; a transmission nodeprovided in each network for transmitting datagrams such that datagramsdestined to an identical destination are transmitted through specificvirtual connections; and a router device for connecting at least two ofthe networks, the router device including: at least one networkinterface connected with said at least two of the networks; table meansfor registering a correspondence between a virtual connection identifierand an output virtual connection identifier; connection identifieranalysis means for determining an output virtual connection identifierfor a datagram entered from one virtual connection, by referring to thetable means according to a virtual connection identifier of said onevirtual connection; and transfer means for transferring the datagramsuch that the datagram is outputted to a virtual connection having theoutput virtual connection identifier determined by the connectionidentifier analysis means.

According to another aspect of the present invention there is provided adata communication network system, comprising: networks including atleast one virtual connection oriented network; a transmission nodeprovided in each network for transmitting datagrams such that datagramswith an identical quality of service are transmitted through specificvirtual connections; and a router device for connecting at least two ofthe networks, the router device including: at least one networkinterface connected with said at least two of the networks; table meansfor registering a correspondence between a virtual connection identifierand a quality of service; connection identifier analysis means fordetermining a quality of service for a datagram entered from one virtualconnection, by referring to the table means according to a virtualconnection identifier of said one virtual connection; scheduler meansfor applying a priority control for datagrams to be transferred by therouter device according to the quality of service determined by theconnection identifier analysis means; and transfer means fortransferring the datagram to which the priority control is applied bythe scheduler means.

According to another aspect of the present invention there is provided adata communication network system, comprising: networks including atleast one ATM network; a transmission node provided in each network fortransmitting datagrams such that datagrams destined to an identicaldestination are transmitted through specific virtual connections; and arouter device for connecting at least two of the networks, the routerdevice including: network interfaces connected with said at least two ofthe networks, each network interface connected with said at least oneATM network including reception means for receiving ATM cellstransmitted from an ATM network and assembling an AAL frame from thereceived ATM cells, and transmission means for forming ATM cells from anAAL frame and transmitting the formed ATM cells to an ATM network; tablemeans for registering a correspondence between a virtual connectionidentifier and a transfer target network interface; connectionidentifier analysis means for determining a transfer target networkinterface for an AAL frame assembled from ATM cells entered from onevirtual connection, by referring to the table means according to avirtual connection identifier of said one virtual connection; processingmeans for determining a transfer target network interface for the AALframe by assembling datagram from the AAL frame and analyzing theassembled datagram, when the table means does not register the transfertarget network interface in correspondence to the virtual connectionidentifier of said one virtual connection; and transfer means fortransferring the AAL frame to the transfer target network interfacedetermined by one of the connection identifier analysis means and theprocessing means.

According to another aspect of the present invention there is provided adata communication network system, comprising: networks including atleast one ATM network; a transmission node provided in each network fortransmitting datagrams such that datagrams destined to an identicaldestination are transmitted through specific virtual connections; and arouter device for connecting at least two of the networks, and fortransferring AAL frames from an ATM network through network interfacesconnected with the networks, each network interface connected with saidat least one ATM network including reception means for receiving ATMcells transmitted from an ATM network and assembling an AAL frame fromthe received ATM cells, and transmission means for forming ATM cellsfrom an AAL frame and transmitting the formed ATM cells to an ATMnetwork, the router device including: table means for registering acorrespondence between a virtual connection identifier and a transfertarget network interface; connection identifier analysis means fordetermining a transfer target network interface for an AAL frameassembled from ATM cells entered from one virtual connection, byreferring to the table means according to a virtual connectionidentifier of said one virtual connection; processing means fordetermining a transfer target network interface for the AAL frame byassembling datagram from the AAL frame and analyzing the assembleddatagram, when the table means does not register the transfer targetnetwork interface in correspondence to the virtual connection identifierof said one virtual connection; and transfer means for transferring theAAL frame to the transfer target network interface determined by one ofthe connection identifier analysis means and the processing means.

According to another aspect of the present invention there is provided adata communication network system, comprising: networks including atleast one ATM network; a transmission node provided in each network fortransmitting datagrams such that datagrams destined to an identicaldestination are transmitted through specific virtual connections; and arouter device for connecting at least two of the networks including anATM network; and an ATM network interface card device for interfacing anATM network and a bus connecting other network interfaces connected withother networks, the ATM network interface card device including:reception means for receiving ATM cells transmitted from the ATM networkand assembling an AAL frame from the received ATM cells; table means forregistering a correspondence between a virtual connection identifier anda transfer target network interface; connection identifier analysismeans for determining a transfer target network interface for one AALframe assembled from ATM cells entered from one virtual connection, byreferring to the table means according to a virtual connectionidentifier of said one virtual connection; and transfer means fortransferring said one AAL frame through the bus to the the transfertarget network interface determined by the connection identifieranalysis means.

According to another aspect of the present invention there is provided adata communication network system, comprising: networks including atleast one ATM network; a transmission node provided in each network fortransmitting datagrams such that datagrams destined to an identicaldestination are transmitted through specific virtual connections; and arouter device for connecting at least two of the networks, the routerdevice including: at least one network interface connected with said atleast two of the networks, each network interface connected with said atleast one ATM network including reception means for receiving ATM cellstransmitted from an ATM network and assembling an AAL frame from thereceived ATM cells, and transmission means for forming ATM cells from anAAL frame and transmitting the formed ATM cells to an ATM network; tablemeans for registering a correspondence between a virtual connectionidentifier and an output virtual connection identifier; connectionidentifier analysis means for determining an output virtual connectionidentifier for an AAL frame assembled from ATM cells entered from onevirtual connection, by referring to the table means according to avirtual connection identifier of said one virtual connection; processingmeans for determining an output virtual connection identifier for theAAL frame by assembling datagram from the AAL frame and analyzing theassembled datagram, when the table means does not register the outputvirtual connection identifier in correspondence to the virtualconnection identifier of said one virtual connection; and transfer meansfor transferring the AAL frame such that the AAL frame is outputted to avirtual connection having the output virtual connection identifierdetermined by one of the connection identifier analysis means and theprocessing means.

According to another aspect of the present invention there is provided adata communication network system, comprising: networks including atleast one virtual connection oriented network; a transmission nodeprovided in each network for transmitting datagrams such that datagramsof an identical protocol type and/or version are transmitted throughspecific virtual connections; and a router device for connecting atleast two of the networks, the router device including: at least onenetwork interface connected with said at least two of the networks;table means for registering a correspondence between a virtualconnection identifier and a protocol type information indicating a typeand/or a version of a protocol; connection identifier analysis means fordetermining a protocol type information for a datagram entered from onevirtual connection, by referring to the table means according to avirtual connection identifier of said one virtual connection; datagramanalysis means for determining a transfer target network interface/nexthop network layer address for the datagram according to a datagramcontent of the datagram, the datagram analysis means having a pluralityof processors in correspondence to different protocols, and the datagramis entered into one of said plurality of processors which corresponds toa protocol of a type and/or a version indicated by the protocol typeinformation determined by the connection identifier analysis means; andtransfer means for transferring the datagram to the transfer targetnetwork interface/next hop network layer address determined by thedatagram analysis means.

According to another aspect of the present invention there is provided atransmission node device for transmitting datagrams to a router device,comprising: table means for registering a correspondence between adestination and an output virtual connection identifier used by therouter device; datagram analysis means for determining an output virtualconnection identifier for a datagram to be transmitted, by referring tothe table means according to a destination of the datagram; andtransmission means for transmitting the datagram to a virtual connectionhaving the output virtual connection identifier determined by thedatagram analysis means, such that datagrams destined to an identicaldestination are transmitted through specific virtual connections.

According to another aspect of the present invention there is provided atransmission node device for transmitting datagrams to a router device,comprising: table means for registering a correspondence between aquality of service specifying information indicating a quality ofservice and an output virtual connection identifier, used by the routerdevice; datagram analysis means for determining an output virtualconnection identifier for a datagram to be transmitted, by referring tothe table means according to a quality of service specifying informationof the datagram; and transmission means for transmitting the datagram toa virtual connection having a virtual connectionn identifier identicalto the output virtual connection identifier determined by the datagramanalysis means, such that datagrams with an identical quality of servicespecifying information are transmitted through specific virtualconnections.

According to another aspect of the present invention there is provided atransmission node device for transmitting datagrams to a router device,comprising: table means for registering a correspondence between aprotocol type information indicating a type and/or a version of aprotocol and an output virtual connection identifier used by the routerdevice; datagram analysis means for determining an output virtualconnection identifier for a datagram to be transmitted, by referring tothe table means according to a type and/or a version of a protocol ofthe datagram; and transmission means for transmitting the datagram to avirtual connection having a virtual connection identifier identical tothe output virtual connection identifier determined by the datagramanalysis means, such that datagrams of an identical protocol type and/orversion are transmitted through specific virtual connections.

According to another aspect of the present invention there is provided amethod for transmitting datagrams to a router device, comprising thesteps of: registering in a table a correspondence between a destinationand an output virtual connection identifier used by the router device;determining an output virtual connection identifier for a datagram to betransmitted, by referring to the table according to a destination of thedatagram; and transmitting the datagram to a virtual connection havingthe output virtual connection identifier determined by the determiningstep, such that datagrams destined to an identical destination aretransmitted through specific virtual connections.

According to another aspect of the present invention there is provided amethod for transmitting datagrams to a router device, comprising thesteps of: registering in a table a correspondence between a quality ofservice specifying information indicating a quality of service and anoutput virtual connection identifier used by the router device;determining an output virtual connection identifier for a datagram to betransmitted, by referring to the table according to a quality of servicespecifying information of the datagram; and transmitting the datagram toa virtual connection having a virtual connection identifier identical tothe output virtual connection identifier determined by the determiningstep, such that datagrams with an identical quality of servicespecifying information are transmitted through specific virtualconnections.

According to another aspect of the present invention there is provided amethod for transmitting datagrams to a router device, comprising thesteps of: registering in a table a correspondence between a protocoltype information indicating a type and/or a version of a protocol and anoutput virtual connection identifier used by the router device;determining an output virtual connection identifier for a datagram to betransmitted, by referring to the table according to a type and/or aversion of a protocol of the datagram; and transmitting the datagram toa virtual connection having a virtual connection identifier identical tothe output virtual connection identifier determined by the determiningstep, such that datagrams of an identical protocol type and/or versionare transmitted through specific virtual connections.

Other features and advantages of the present invention will becomeapparent from the following description taken in conjunction with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of one conventional router device.

FIG. 2 is a schematic block diagram of another conventional routerdevice.

FIG. 3 is a schematic block diagram of a transmission node in the datacommunication network system used for the present invention.

FIG. 4 is a block diagram of a router device in the first embodiment ofthe present invention.

FIG. 5 is a diagram showing a routing table in the datagram analysisunit of the router device of FIG. 4.

FIG. 6 is a diagram showing a transfer table in the connectionidentifier analysis unit of the router device of FIG. 4.

FIG. 7 is a block diagram showing an exemplary operation in the routerdevice of FIG. 4.

FIG. 8 is a block diagram of one modified configuration for the-routerdevice in the first embodiment of the present invention.

FIG. 9 is a block diagram of another modified configuration for therouter device in the first embodiment of the present invention.

FIG. 10 is a block diagram of a router device in the second embodimentof the present invention.

FIG. 11 is a diagram showing a QOS table in the connection identifieranalysis unit of the router device of FIG. 10.

FIG. 12 is a block diagram showing an exemplary operation in the routerdevice of FIG. 10.

FIG. 13 is a block diagram of one modified configuration for the routerdevice in the second embodiment of the present invention.

FIG. 14 is a block diagram of a router device in the third embodiment ofthe present invention.

FIG. 15 is a block diagram of one modified configuration for the routerdevice in the third embodiment of the present invention.

FIG. 16 is a block diagram of a router device in the fourth embodimentof the present invention.

FIG. 17 is a block diagram of one modified configuration for the routerdevice in the fourth embodiment of the present invention.

FIG. 18 is a schematic block diagram of another modified configurationfor the router device in the fourth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, various embodiments of a router device and a datagram transfermethod according to the present invention will be described withreferences to the drawings.

First, a prerequisite concerning a data communication network systemwill be described.

In short, the present invention carries out the datagram transfer at arouter device by referring to a virtual connection identifier of areceived datalink frame, instead of the datagram transfer based on anetwork layer address of a transfer target that can be obtained byreferring to datagram content extracted from a received datalink frame.

In order to make it possible to determine a transfer target of thedatagram according to a virtual connection identifier of a receiveddatalink frame, it is necessary to make each datagram transmission nodeto transmit a specific type of datagrams only through specific virtualconnections, such that only a specific type of datagrams are transmittedthrough these specific virtual connections.

Here, a specific type of datagrams can be any of the following threetypes of datagrams according to the need:

-   -   Type I: Datagrams destined to a specific destination;    -   Type II: Datagrams with a specific QOS (Quality Of Service); and    -   Type III: Datagrams of a specific protocol type or a specific        protocol version.

Type I datagrams destined to a specific destination can include thosedatagrams which have an identical destination address, or thosedatagrams which have an identical value for a logical product of adestination address and a mask, for example.

Type II datagrams with a specific QOS can include those datagrams whichhave identical values for one or more of the following QOS specifyinginformation, for example.

-   -   (1) Protocol type (such as IP, IPX)    -   (2) IP version (such as IPv4, IPv6)    -   (3) Protocol identifier (such as TCP, UDP)    -   (4) Destination address    -   (5) Logical product of destination address and mask    -   (6) Destination transport layer port    -   (7) Source address    -   (8) Logical product of source address and mask    -   (9) Source transport layer port    -   (10) Stream ID for ST-2 (in a case of IPv5)    -   (11) Flow ID (in a case of IPv6)    -   (12) TOS (Type Of Service) (in a case of IPv4)    -   (13) Traffic class (in a case of IPv6)

Note that each of the above QOS specifying informations (9) to (13) isan information usually used to define QOS, while each of the above QOSspecifying informations (1) to (8) is an information that can be used asan indication of QOS.

For example, in a case of using the QOS specifying information (1),datagrams of the protocol type IP can be associated with a particularQOS so that they can form one specific type of datagrams to betransmitted only through some specific virtual connections, whiledatagrams of the protocol IPX can be associated with another particularQOS so that they can form another specific type of datagrams to betransmitted only through some other specific virtual connections.

Similarly, in a case of using the QOS specifying information (4),datagrams destined to one particular destination can be associated witha particular QOS so that they can form one specific type of datagrams tobe transmitted only through some specific virtual connections, whiledatagrams destined to any other destinations can be associated withanother particular QOS so that they can form another specific type ofdatagrams to be transmitted only through some other specific virtualconnections.

Type III datagrams of a specific protocol type or a specific protocolversion can include those datagrams which have an identical protocoltype such as IP or IPX, or those datagrams which have an identical IPversion such as IPv4 or IPv6, for example.

In order to transmit a specific type of datagrams only through specificvirtual connections, it is possible to use a transmission node having aconfiguration as shown in FIG. 3, which comprises a datagram analysisunit 1 having a routing table 2, and an interface (I/F) 3 having atransmission unit 4 connected between the datagram analysis unit 1 and avirtual connection oriented LAN 41. Note that FIG. 3 shows an exemplarycase of classifying datagrams according to their destinations and QOSs,so that the routing table 2 shown in FIG. 3 has a field for adestination and a field for a QOS specifying information along withfields for an output I/F and an output virtual connection identifier,but a field for a destination or a field for a QOS specifyinginformation may be omitted if unnecessary, and a QOS specifyinginformation can be given by any one or more of QOS specifyinginformation (1) to (13) enumerated above so as to realize any desiredclassification of datagrams. Note also that FIG. 3 shows only one I/F 3for the sake of simplicity, but the transmission node may actually haveas many I/Fs as necessary.

Here, a procedure for this transmission node of FIG. 1 to outputdatagram according to its destination will be described.

For example, in a case of transmitting a datagram to a destination A,the datagram analysis unit 1 refers to the routing table 2 whichregisters a correspondence among the destination, the output I/F, andthe output virtual connection identifier, by using the destination A asa key, and determines that, for this datagram to the destination A, theoutput I/F is “atm1” and the output virtual connection is a virtualconnection with a virtual connection identifier “1”. Accordingly, thedatagram analysis unit 1 sends this datagram to the I/F 3 correspondingto “atm1”. Then, the transmission unit 4 of this I/F 3 assembles an AALframe which is the datalink frame from the received datagram, dividesthe assembled AAL frame into ATM cells, and outputs the ATM cells to thevirtual connection with a virtual connection identifier “1” in thevirtual connection oriented LAN 41.

Note that the datagram analysis unit 1 searches through the routingtable 2 by using “destination” as a key in the above description, but itis also possible to provide a routing table which can be searchedthrough by using other information such as “quality of service” or“source address” as a key.

In the following description of the various embodiments of a routerdevice according to the present invention, it is assumed that a datacommunication network system uses transmission nodes of a type shown inFIG. 3 described above, so that a specific type of datagrams aretransmitted only through specific virtual connections.

Also, in the following, the virtual connection oriented network can be anetwork in which nodes are connected through ATM switches, or a networkin which nodes are connected through point-to-point links without usingATM switches.

Also, in the following, the networks to which the interfaces areconnected can be physical networks, or logical networks. In the lattercase, the logical networks may belong to a single physical network, or aplurality of physical networks.

Also, in the following, the interface is not necessarily limited to aphysical interface, and may include an interface function realized onCPU by means of software.

Now, with references to FIG. 4 to FIG. 9, the first embodiment of arouter device according to the present invention will be described indetail.

In the following description of this first embodiment, it is supposedthat the router device is connected with two virtual connection orientedLANs 41 and 42 as well as one non-virtual connection oriented LAN 43 forthe sake of definiteness. Here, the virtual connection oriented LAN isassumed to be an ATM-LAN and the non-virtual connection oriented LAN isassumed to be an Ethernet for the sake of explanation.

As shown in FIG. 4, the router device of this first embodiment has aninterface (I/F) 10 including a reception unit 11 and a transmission unit13, a datagram analysis unit 21 connected with the reception unit 11,and a datagram processing unit 22 connected with the transmission unit13, all in correspondence to each LAN connected to this router device.In addition, the interface 10 connected to the virtual connectionoriented LAN 41 or 42 further includes a connection identifier analysisunit 12 connected between the reception unit 11 and the datagramanalysis unit 21. The router device also has a transfer unit 30connected with each datagram analysis unit 21, each datagram processingunit 22, and each connection identifier analysis unit 12, so as tomutually connect sections corresponding to different LANs. In thefigure, subscripts attached to the reference numeral are used todistinguish similar elements provided in correspondence to differentLANs.

In the following description of this first embodiment, the networkprotocol for transferring the datagram is assumed to be IP (InternetProtocol) for the sake of definiteness, although the present inventionis equally applicable to any network protocol other than IP such as IPX.

The reception unit 11 receives the datalink frame from a connected LAN,and applies a processing appropriate for that LAN.

In a case of the Ethernet LAN, the reception unit 11 extracts thedatalink frame destined to itself, and applies a CRC check for detectingerrors in the datalink frame. Then, the reception unit 11 constructs thedatagram from the datalink frame and determines which network protocolis to be used according to the datalink frame. Then, the constructeddatagram and the received virtual connection identifier are given to theconnection identifier analysis unit 12.

On the other hand, in a case of the ATM-LAN, the reception unit 11detects errors in the ATM cells, assembles the AAL frame, carries outthe error detection, determines which network protocol is to be used,and constructs the datagram. Then, the constructed datagram and thereceived VPI/VCI are given to the connection identifier analysis unit12.

The datagram analysis unit 21 determines an output interface and anetwork layer address of a next hop node by referring to datagramcontent (including a header information such as a source address, adestination address, a flow ID, and TOS, and an upper layer informationsuch as a port address). In order to realize this function, the datagramanalysis unit 21 is provided with a routing table 210 as shown in FIG.5, which registers the output interface and the next hop network layeraddress in correspondence to each datagram destination address. In thisrouting table 210, the output virtual connection identifier isregistered instead of the next hop network layer address when the outputinterface is the virtual connection oriented LAN.

In the routing table 210 shown in FIG. 5, in order to explain both acase in which the next hop network layer address is registered in therouting table 210 and a case in which the output virtual connectionidentifier is registered in the routing table 210, the routing table 210registers the next hop network layer address when the output interfaceis the non-virtual connection oriented LAN, or the output virtualconnection identifier when the output interface is the virtualconnection oriented LAN.

The datagram analysis unit 21 gives the datagram to the datagramprocessing unit 22 connected with the output interface determinedaccording to this routing table 210, via the transfer unit 30.

Note that the routing table 210 shown in FIG. 5 is to be referred byusing only the destination address as a key, but it is also possible toprovide a routing table which can be searched through by using otherdatagram content as enumerated above as a key.

The connection identifier analysis unit 12 is provided only in theinterface 10 connected with the virtual connection oriented LAN. Unlikethe datagram analysis unit 21 which determined the output interface fromthe datagram content, the connection identifier analysis unit 12determines the output interface by referring to the virtual connectionidentifier of the received datalink frame rather than the datagramcontent. In addition, the next hop network layer address or the outputvirtual connection identifier may also be determined by the connectionidentifier analysis unit 12. In order to realize this function, theconnection identifier analysis unit 12 is provided with a transfer table120 as shown in FIG. 6, which registers the output interface and thenext hop network layer address in correspondence to each inputconnection identifier. In this transfer table 120, the output virtualconnection identifier is registered instead of the next hop networklayer address when the output interface is the virtual connectionoriented LAN.

This transfer table 120 may be prepared manually, or automatically bymeans of a protocol with respect to the transmission node. This transfertable 120 can be constructed automatically by exchanging the virtualconnection identifier and a type (such as a destination network layeraddress or a transport layer port) of datagram conveyed by that virtualconnection between this router device and neighboring nodes.

The connection identifier analysis unit 12 determines whether thedatagram should be sent to the datagram analysis unit 21 or to thedatagram processing unit 22 of the interface 10 for transmitting thisdatagram via the transfer unit 30, according to this transfer table 120.Namely, the datagram received via the connection registered in thistransfer table 120 will be given to the datagram processing unit 22belonging to the corresponding output interface. On the other hand, adatalink frame which has a connection identifier not registered in thistransfer table 120 or a datagram which has description indicating thatis it to be given to the datagram analysis unit 21 will be given to thedatagram analysis unit 21 so as to refer to its datagram content there.

The transfer unit 30 receives the datagram from the datagram analysisunit 21 or the connection identifier analysis unit 12, and gives thatdatagram to the datagram processing unit 22 belonging to the specifiedoutput interface. At this point, in addition to the datagram itself, thenext hop network layer address or the output virtual connectionidentifier searched out from the routing table 210 of the datagramanalysis unit 21 or the transfer table 120 of the connection identifieranalysis unit 12 is also given to the datagram processing unit 22. Thistransfer unit 30 can be constructed from a bus or a switch, for example.

The datagram processing unit 22 carries out a processing to rewrite aheader of the datagram (including a processing to reduce TTL (Time ToLive), a checksum calculation, an optional processing, etc. in a case ofIP). Also, when the datagram is larger than a maximum frame length ofthe LAN, the datagram processing unit 22 divides the datagram into partswhich fit to the maximum frame length of the LAN. The actual processingcontents of these processings may differ depending on which networkprotocol is used.

The transmission unit 13 carries out the processing appropriate for aconnected LAN, in order to transmit the datagram to that LAN. Forexample, in a case of the ATM-LAN, the datagram is changed to thedatalink frame (AAL frame), divided into ATM cell sizes, and outputtedby attaching the specified output connection identifier.

When the output virtual connection identifier is not specified in boththe routing table 210 and the transfer table 120, the network layeraddress of the next hop node is specified at the routing table 210 orthe transfer table 120. Then, the output virtual connection identifieris determined from the specified network layer address of the next hopnode by referring to a table provided in the transmission unit 13, whichregisters a correspondence between the network layer address and thevirtual connection identifier. The cells are then outputted to the LANby using the output virtual connection identifier determined in thismanner.

When the output virtual connection identifier is obtained from therouting table 210 or the transfer table 120, the ATM cells areconstructed from the datagram and outputted to the LAN by using theobtained output virtual connection identifier.

Next, the datagram transfer operation in the router device of this firstembodiment will be described with reference to FIG. 7.

Suppose now that I/F1 has three virtual connections (virtualconnection-1, virtual connection-2, and virtual connection-10) set upand I/F2 has one virtual connection (virtual connection-3) set up asshown in FIG. 7, while the transfer table 120 of the connectionidentifier analysis unit 12 and the routing table 210 of the datagramanalysis unit 21 for I/F1 are set up as shown in FIG. 7. These settingsmay be made manually, or automatically by means of a protocol, similarlyas described above in conjunction with the transfer table 120 of theconnection identifier analysis unit 12.

Also, suppose that the virtual connection-1 is set to transmit onlydatagrams destined to the destination A, and the virtual connection-2 isset to transmit only datagrams destined to the destination B. Thesesettings can be realized by using the transmission node shown in FIG. 3described above. The destination A is assumed to be located in adirection of I/F2, and the destination B is assumed to be located in adirection of I/F3. Note that the setting used here requires thetransmission of only datagrams destined to one destination through onevirtual connection, but it is also possible to use the setting whichrequires the transmission of only datagrams having identical sourceaddress and identical destination address through one virtual connectionby means of the transmission node shown in FIG. 3 described above, forexample, such that only a specific type of datagrams can be transmittedbetween the router device and its neighboring nodes.

Then suppose that the datagram is transmitted through the virtualconnection-1. First, the reception unit 11 receives this datagram, andgives the received datagram and the virtual connection identifier of thevirtual connection-1 to the connection identifier analysis unit 12 ₁.

The connection identifier analysis unit 12 ₁ can recognize that thisdatagram is a datagram entered from the virtual connection-1, so thatthe connection identifier analysis unit 12 ₁ refers to the transfertable 120 ₁ by using the input connection identifier “1” of the virtualconnection-1 as a key. As a result, it can be determined that thisdatagram should be outputted to the virtual connection-3 of I/F2. Inthis manner, according this first embodiment, it is possible todetermine the output target without referring to the datagram content.

When the output target is determined in this manner, this datagram andthe output virtual connection identifier “3” of the virtual connection-3as the output virtual connection identifier are given to the datagramprocessing unit 22 ₂ of I/F2 via the transfer unit 30. Then, after thenetwork layer processing is applied at the datagram processing unit 22₂, this datagram is transmitted from the transmission unit 13 ₂ to thevirtual connection-3 as determined from the transfer table 120 ₁. Inthis manner, the transfer from one virtual connection oriented LAN 41 toanother virtual connection oriented LAN 42 can be completed.

If the network layer address of the next hop node rather than the outputvirtual connection identifier is given in the transfer table 120 of theconnection identifier analysis unit 12, the transfer unit 30 gives thedatagram and the network layer address of the next hop node to thedatagram processing unit 22. Then, the datagram is given from thedatagram processing unit 22 to the transmission unit 13 after thenetwork layer processing is applied to the datagram at the datagramprocessing unit 22. The transmission unit 13 then determines the outputvirtual connection identifier from the network layer address of the nexthop node, and transmits the datagram to the LAN.

Next, a case of transfer from the virtual connection oriented LAN to thenon-virtual connection oriented LAN will be described.

Suppose here that the datagram is transmitted through the virtualconnection-2 of I/F1. After this datagram is received at the receptionunit 11 ₁, the connection identifier analysis unit 12 ₁ refers to thetransfer table 120 ₁ by using the input connection identifier “2” of thevirtual connection-2 as a key. As a result, it can be determined thatthis datagram should be outputted from the output I/F3 to the next hopnetwork layer address C.

The connection identifier analysis unit 12 ₁ then gives this datagramand the network layer address C of the next hop node to the datagramprocessing unit 22 ₃ of I/F3 via the transfer unit 30. Then, after thenetwork layer processing is applied at the datagram processing unit 22₃, this datagram and the network layer address C of the next hop nodeare given to the transmission unit 13 ₃. The transmission unit 13 ₃ thendetermines the datalink address from the network layer address of thenext hop node, and transmits the datagram to the LAN.

In the above, the transfer target is determined by using the connectionidentifier, without referring to the datagram content, but it is alsopossible to use a conventional scheme here. Namely, when the transfertarget cannot be determined from the connection identifier at theconnection identifier analysis unit 12 ₁, the datagram can be given tothe datagram analysis unit 21 ₁ so that the transfer target can bedetermined from the datagram content there.

For example, the datalink frame entered from the virtual connection-10is received by the reception unit 11 ₁, and after being changed into thedatagram there, the transfer table 120 ¹ is referred at the connectionidentifier analysis unit 12 ₁. In this case, the transfer table 120 ₁has no corresponding entry registered, so that the datagram is given tothe datagram analysis unit 21 ₁. Also, when the transfer table 120 ₁ hasan indication that this datagram should be given to the datagramanalysis unit 21 ₁, the datagram is given to the datagram analysis unit21 ₁ similarly.

The datagram analysis unit 21 ₁ then refers to the datagram content, andrecognizes that this datagram is destined to the destination B. Then,the datagram analysis unit 21 ₁ refers to the routing table 210 ₁ andrecognizes that the datagram destined to the destination B should beoutputted from I/F3 to the next hop network layer address C.Accordingly, the datagram and the network layer address C of the nexthop node are given to the datagram processing unit 22 ₃ of I/F3 via thetransfer unit 30, and then outputted from the transmission unit 13 ₃ tothe non-virtual connection oriented LAN 43.

In this manner, it is possible for the router device to determine thedestination address of the input datagram from the virtual connectionidentifier of the virtual connection through which the datagram isentered.

Consequently, an output interface and an address of a next hop router oran output virtual connection identifier in a case where an output targetis a virtual connection network can be determined at the router devicewithout looking into the datagram content, and therefore it is possibleto improve the transfer efficiency at the router device.

It is to be noted that FIG. 4 shows an example in which the datagramanalysis unit 21 and the datagram processing unit 22 are provided incorrespondence to each interface 10, but a configuration of FIG. 4 canbe modified to share a single set of the datagram analysis unit 21 andthe datagram processing unit 22 among a plurality of interfaces 10, asshown in FIG. 8.

Here, a procedure for carrying out the datagram transfer in this routerdevice of FIG. 8 will be described.

In this case, the detailed operation of each element in this routerdevice of FIG. 8 is similar to that described above for the routerdevice of FIG. 4.

Suppose now that the virtual connection-1 is set to transmit onlydatagrams destined to the destination D, and the virtual connection-10is set to transmit various types of datagrams destined to differentdestinations. These settings can be realized by using the transmissionnode shown in FIG. 3 described above.

When the datalink frame is entered from the virtual connection-1, thereception unit 11 ₂ changes the received datalink frame into thedatagram. Then, the transfer table 120 ₂ is referred at the connectionidentifier analysis unit 12 ₂ to determine that the datagram receivedfrom the virtual connection-1 should be outputted from I/F3 to the nexthop network layer address C. After that, the datagram is given to thedatagram processing unit 22 via the transfer unit 30, and then to thetransmission unit 13 ₃ via the transfer unit 30, and outputted fromthere similarly as in an exemplary case of FIG. 7 described above.

On the other hand, when the datalink frame is received from the virtualconnection-10, the reception unit 11 ₂ changes the received datalinkframe into the datagram. Then, the transfer table 120 ₂ is referred atthe connection identifier analysis unit 12 ₂. As a result, when it isconfirmed that this virtual connection-10 is not registered in thistransfer table 120 ₂, the datagram is given to the datagram analysisunit 21 via the transfer unit 30. Then, the datagram analysis unit 21refers to the routing table 210 to determine that this datagram shouldbe outputted from I/F3 to the next hop network layer address B. Then,similarly as in the above, the datagram is given to the datagramprocessing unit 22 via the transfer unit 30, and then to thetransmission unit 13 ₃ via the transfer unit 30, and outputted fromthere.

It is also to be noted that a configuration of FIG. 8 can be furthermodified as shown in FIG. 9. Namely, in this router device of FIG. 9,the function to change the datalink frame into the datagram and thefunction to change the datagram into the datalink frame are removed fromthe reception unit 11 and the transmission unit 13, respectively, and adatalink frame/datagram conversion unit 50 having these functions areadditionally provided between the transfer unit 30 and the datagramanalysis unit 21 and between the transfer unit 30 and the datagramprocessing unit 22.

In this case, the operation since the datalink frame is entered from thevirtual connection-1 or the virtual connection-10 until it istransmitted from the transmission unit 13 ₃ is basically similar to thatin a case of the router device of FIG. 8 described above, except for theoperation of the datalink frame/datagram conversion unit 50 which takesplace between the operations of the transfer unit 30 and the datagramanalysis unit 21 and between the operation of the transfer unit 30 andthe datagram processing unit 22.

In this modified configuration of FIG. 9, unlike a configuration of FIG.8, there are cases in which the processings at the datagram analysisunit 21, the datagram processing unit 22, and the datalinkframe/datagram conversion unit 50 can be omitted while transferringdata.

For example, the datalink frame received from the virtual connection-2of I/F2 is applied with the datalink layer processing such as thedatalink checksum calculation at the reception unit. 11 ₂, and then thetransfer table 120 ₂ is referred at the connection identifier analysisunit 12 ₂. As a result, it can be determined that this datalink frameshould be outputted to the virtual connection-3 of I/F1. In this case,this datalink frame is then given to the transmission unit 13 ₁ via thetransfer unit 30, and after the datalink layer processing is applied atthe transmission unit 13 ₁, this datalink frame is outputted to thevirtual connection oriented LAN 41, so that this datalink frame can betransferred without requiring the processings at the datagram analysisunit 21, the datagram processing unit 22, and the datalinkframe/datagram conversion unit 50.

It is to be noted that, in the first embodiment described above, thetransfer table 120 of the connection identifier analysis unit 12 is usedfor determining an output interface to which the datagram is to betransferred, but it is also possible to use the transfer table 120 ofthe connection identifier analysis unit 12 for determining an outputvirtual connection identifier corresponding to an input connectionidentifier, and transfer the datagram such that the datagram isoutputted to a virtual connection having a virtual connection identifieridentical to the determined output virtual connection identifier, in thesimilar manner as described above.

It is also to be noted that, in the first embodiment described above,the output interface and the network hop network layer address aresearched out from the transfer table 120 of the connection identifieranalysis unit 12 by using the input connection identifier as a key, butit is also possible to modify the above first embodiment such that theconnection identifier analysis unit has a table for registering acorrespondence between an input virtual connection identifier and aprotocol type information indicating a type and/or a version of aprotocol of the datagram, such that a protocol type and/or version canbe searched out from this table of the connection identifier analysisunit by using the input connection identifier as a key.

In this case, the output interface cannot be determined by theconnection identifier analysis unit, so that all the datagrams will besent to the datagram analysis unit to determine their appropriate outputinterfaces. Here, however, the datagram analysis unit can recognize theprotocol of the received datagram before the datagram content isreferred by means of the operation by the connection identifier analysisunit.

In general, the datagram analysis unit can have a multiprocessorconfiguration formed by a plurality of processors, which are provided incorrespondence to different protocols. In such a case, the datagramanalysis unit can enter the received datagram into an appropriateprocessor corresponding to the protocol of that datagram, withoutreferring to the datagram content, so that there is no need for anoperation to classify the received datagrams according to theirprotocols at the datagram analysis unit.

For example, when the datagram analysis unit has one processorresponsible for the datagram analysis and processing of datagrams of IP(or IPv6) and another processor responsible for the datagram analysisand processing of datagrams of IPX (or IPv4), the datagram entering intothe datagram analysis unit can be appropriately entered into thecorresponding processor according to the protocol type and/or version ofthe datagram determined by the connection identifier analysis unitaccording to the input connection identifier of the datagram.

Referring now to FIG. 10 to FIG. 13, the second embodiment of a routerdevice according to the present invention will be described in detail.

In this second embodiment, the router device has a configuration asshown in FIG. 10, where the reception unit 11, the connection identifieranalysis unit 12, the transmission unit 13, the datagram analysis unit21, the datagram processing unit 22, and the transfer unit 30 arebasically similar to those in the first embodiment described above,except that the connection identifier analysis unit 12 has a modifiedinternal configuration as will be described below. Here, the datagramanalysis unit 21 and the datagram processing unit 22 are shared among aplurality of interfaces similarly as in a configuration of FIG. 8described above.

In addition, this router device of FIG. 10 has a scheduler 60 connectedbetween the connection identifier analysis unit 12 and the transfer unit30, and a scheduler connected between the transfer unit 30 and thetransmission unit 13.

The router device of FIG. 10 is connected with two virtual connectionoriented LANs 41 and 42 as well as one non-virtual connection orientedLAN 43 similarly as in the first embodiment described above.

This second embodiment differs from the first embodiment described abovein the incorporation of the schedulers 60 and 61, and the internalconfiguration of the connection identifier analysis unit 12.

Each one of the schedulers 60 and 61 changes an output order of thedatagrams according to the requested quality of service of eachdatagram, instead of outputting the datagrams in the received order. Forexample, the output order of the datagrams can be changed by separatelystoring the datagrams in buffers provided in correspondence to differentlevels of quality of service, and changing a rate of extracting thedatagrams from each buffer according to the corresponding quality ofservice.

On the other hand, the connection identifier analysis unit 12 isprovided with a QOS table 126 as shown in FIG. 11, which registers thequality of service (QOS) in correspondence to each input connectionidentifier, instead of the transfer table used in the first embodimentdescribed above. By changing this QOS table 126, the information thatcan be determined from the input connection identifier can be changed.

Next, the datagram transfer operation in the router device of thissecond embodiment will be described with reference to FIG. 12.

Suppose now that I/F1 has three virtual connections (virtualconnection-1, virtual connection-2, and virtual connection-10) set up asshown in FIG. 12, where the virtual connection-1 is set to transmit onlydatagrams of QOS-1, and the virtual connection-2 is set to transmit onlydatagrams of QOS-2. These settings can be realized by using thetransmission node shown in FIG. 3 described above. Here, the QOS-1 isassumed to be in a higher priority level than the QOS-2.

Suppose also that the QOS table 126 of the connection identifieranalysis unit 12 for I/F1 and the routing table 210 of the datagramanalysis unit 21 are set up as shown in FIG. 12. The QOS table 126 shownin FIG. 12 indicates that the virtual connection-1 corresponds to theQOS-1, and the virtual connection-2 corresponds to the QOS-2. Thesesettings may be made manually, or automatically by means of a protocol.This QOS table 126 can be constructed automatically by exchanging thevirtual connection identifier and a quality of service of datagramconveyed by that virtual connection between this router device andneighboring nodes.

Then, when the datagram is received from the virtual connection-1, thereception unit 11 ₁ receives this datagram, and applies the datalinklayer processing. After that, the connection identifier analysis unit 12₁, refers to the QOS table 126 ₁ i by using the input connectionidentifier “1” of the virtual connection-1 as a key. As a result, it canbe determined that this datagram is of the QOS-1. In this manner,according this second embodiment, it is possible to determine thequality of service without referring to the datagram content.

Next, the scheduler 60 ₁ enters this datagram into a buffer-1 providedtherein in correspondence to the QOS-1. The scheduler 60 ₁ extracts thedatagrams from the buffers according to the priority order among thedatagrams, and sends the datagrams to the datagram analysis unit 21 viathe transfer unit 30. Here, an order of extracting can be set such thatany datagrams of QOS-1 at a higher priority order existing in thebuffers are extracted first, and any datagram of QOS-2 are extractedafter that.

The datagram extracted from the buffers in the scheduler 60 ₁ is thengiven to the datagram analysis unit 21 to determine the output interfaceand the network layer address of the next hop node from the destinationof the datagram by referring to the routing table 210, and then given tothe datagram processing unit 22. After that, the datagram is given tothe scheduler 61 ₂ of the output target, and then given to thetransmission unit 13 ₂, and outputted from there to complete thetransfer. Here, the datagram transfer from the scheduler 61 ₂ to thetransmission unit 13 ₂ in the output interface is also carried outaccording to the priority order similarly as in a case of the scheduler60, described above.

Similarly, the datagram entered from the virtual connection-2 isreceived by the reception unit 11 ₁, and determined that it is of theQOS-2 by referring to the QOS table 126 ₁ at the connection identifieranalysis unit 12 ₁. Then, this datagram is entered into a bufferprovided in correspondence to the QOS-2 at the scheduler 60 ₁, andthereafter processed similarly as the datagram of QOS-1 described above.

As for the datagram entered from the virtual connection-10, the QOStable 126 ₁ of the connection identifier analysis unit 12 ₁ does notregister a corresponding virtual connection identifier, so that thisdatagram is entered into a buffer provided in correspondence to thelowest priority order at the scheduler 60 ₁, and thereafter processedsimilarly as the datagram of QOS-1 described above.

In this manner, it is possible for the router device to determine theQOS class of the input datagram from the virtual connection identifierof the virtual connection through which the datagram is entered.Consequently, the datagrams can be classified according to their QOSclasses at the router device without looking into the datagram content.By means of this, at a time of datagram scheduling at an input stage, itbecomes possible to realize the scheduling according to the QOS classeseven if the processings of the transfer unit 30, the datagram analysisunit 21, and the datagram processing unit 22 are slow.

It is to be noted that a configuration of FIG. 10 can be modified toincorporate the datagram analysis unit 21 and the datagram processingunit 22 for each interface separately as shown in FIG. 13. In thismodified configuration of FIG. 13, the received datalink frame isapplied with the datalink layer processing at the reception unit 11, andthe quality of service is determined from the QOS table 126 at theconnection identifier analysis unit 12, and the datagram is given to thescheduler 60 according to the determined quality of service, similarlyas in a case of FIG. 12 described above.

In this modified configuration of FIG. 13, however, the datagramoutputted from the scheduler 60 is given to the datagram analysis unit21 and the output interface and the network layer address of the nexthop node or the output virtual connection identifier are determined fromthe destination address of the datagram there. After that, the datagramis transferred to the datagram processing unit 22 of the outputinterface via the transfer unit 30, and then given to the scheduler 61and outputted from the transmission unit 13 in the output interface.Here, the datagram transfer from the scheduler 61 to the transmissionunit 13 in the output interface is also carried out according to thepriority order similarly as in a case of the scheduler 60 describedabove.

Referring now to FIG. 14 and FIG. 15, the third embodiment of a routerdevice according to the present invention will be described in detail.

This third embodiment is a combination of the first and secondembodiments described above, in which both the transfer target and thequality of service can be determined without referring to the datagramcontent.

In this third embodiment, the router device has a configuration as shownin FIG. 14, where the reception unit 11, the connection identifieranalysis unit 12, the transmission unit 13, the datagram analysis unit21, the datagram processing unit 22, the transfer unit 30, and theschedulers 60 and 61 are basically similar to those in the secondembodiment described above, except that the connection identifieranalysis unit 12 has a modified internal configuration as will bedescribed below. Here, the datagram analysis unit 21 and the datagramprocessing unit 22 are shared among a plurality of interfaces similarlyas in a configuration of FIG. 8 described above.

This router device of FIG. 14 is connected with two virtual connectionoriented LANs 41 and 42 as well as one non-virtual connection orientedLAN 43 similarly as in the first and second embodiments described above.

The connection identifier analysis unit 12 is provided with a transfertable 129 as shown in FIG. 14, which registers the quality of service(QOS), the output interface (output I/F), and the next hop network layeraddress or the output virtual connection identifier (address) incorrespondence to each input connection identifier (input), so that thistransfer table 129 combines the transfer table 120 of the firstembodiment and the QOS table 126 of the second embodiment.

Next, the datagram transfer operation in the router device of this thirdembodiment will be described with reference to FIG. 14.

Suppose now that I/F1 has the virtual connection-1 which is set totransmit only datagrams of QOS-1 destined to the destination A, and thevirtual connection-2 which is set to transmit only datagrams of QOS-2.These settings can be realized by using the transmission node shown inFIG. 3 described above. Here, the QOS-1 is assumed to be in a higherpriority level than the QOS-2.

Suppose also that the transfer table 129 of the connection identifieranalysis unit 12 for I/F1 and the routing table 210 of the datagramanalysis unit 21 are set up as shown in FIG. 14.

Then, when the datagram is received from the virtual connection-1 at thereception unit 11, of I/F1, the datalink layer processing is applied tothis datagram there, and this datagram is given to the connectionidentifier analysis unit 12 ₁. Then, the connection identifier analysisunit 12 ₁ refers to the transfer table 129 ₁ by using the inputconnection identifier “1” of the virtual connection-1 as a key. As aresult, it can be determined that this datagram is of the QOS-1, forwhich the output interface is I/F2 and the output virtual connection isthe virtual connection-3.

Next, this datagram is entered into a buffer-1 provided incorrespondence to the QOS-1 in the scheduler 60 ₁ to receive thetransfer order priority control by the the scheduler 60 ₁, and thengiven to the transfer unit 30 along with the output virtual connectionidentifier “3”.

Then, this datagram is given to the datagram processing unit 22 andapplied with the network layer processing there, and then given to thescheduler 61 ₂ of I/F2 via the transfer unit 30 to receive the transferorder priority control there. This datagram is then given to thetransmission unit 13 ₂, and outputted to the virtual connection-3 fromthere.

In the above description, the datagram and the virtual connectionidentifier “3” are given from the scheduler 60 to the transfer unit 30,but the quality of service QOS-1 may also be given in addition to themfor use in the priority control at the scheduler 61 ₂.

Similarly, the datagram entered from the virtual connection-2 isreceived by the reception unit 11 ₁, and given to the connectionidentifier analysis unit 12 ₁. Then, by referring to the transfer table129 ₁ at the connection identifier analysis unit 12 ₁, it can bedetermined that this datagram is of the QOS-2 for which the output I/Fand the address are not specified.

Consequently, this datagram is entered into a buffer provided incorrespondence to the QOS-2 at the scheduler 60 ₁, and as the output I/Fis not determined yet, this datagram is given to the datagram analysisunit 21 via the transfer unit 30. The datagram analysis unit 21 thenrefers to the destination of this datagram, and when it is recognizedthat this datagram is destined to the destination B, the routing table210 is referred by using this destination B as a key, to determine thatthe output interface is I/F3 and the network layer address of the nexthop node is D in this case.

Then, this datagram is given to the datagram processing unit 22 ₃ andapplied with the network layer processing there, and then given to thescheduler 61 ₃ of I/F3 via the transfer unit 30 to receive the transferorder priority control there. Then, at the transmission unit 13 ₃, thedatalink address is determined from the next hop network layer address,the datalink frame is constructed, and outputted to the LAN from there.

In this manner, it is possible for the router device to determine thedestination address and the quality of service of the input datagramfrom the virtual connection identifier of the virtual connection throughwhich the datagram is entered. Consequently, it is possible to improvethe transfer efficiency at the router device considerably.

It is to be noted that a configuration of FIG. 14 can be modified toincorporate the datagram analysis unit 21 and the datagram processingunit 22 for each interface separately as shown in FIG. 15.

In this modified configuration of FIG. 15, the received datalink frameis applied with the datalink layer processing at the reception unit 11,and the destination address and the quality of service are determinedfrom the transfer table 129 at the connection identifier analysis unit12, and the datagram is given to the scheduler 60 according to thedetermined quality of service, similarly as in a case of FIG. 14described above.

In this modified configuration of FIG. 15, however, the scheduler 60determines whether the datagram should be given to the datagram analysisunit 21 or the transfer unit 30. When the virtual connection-1 is set totransmit only dataagrams of QOS-1 destined to the destination A, and thevirtual connection-2 is set to transmit only datagrams of QOS-2 as in acase of FIG. 14, the output interface and the next hop network layeraddress or output virtual connection identifier can be determined fromthe transfer table 129 of the connection identifier analysis unit 12 forthe datagram received from the virtual connection-1, so that thisdatagram and the next hop network layer address or output virtualconnection identifier are given to the datagram processing unit 22 ofthe output interface via the transfer unit 30.

On the other hand, the output interface and the next hop network layeraddress or output virtual connection identifier cannot be determinedfrom the transfer table 129 of the connection identifier analysis unit12 for the datagram received from the virtual connection-2. For thisreason, this datagram is given to the datagram analysis unit 21, and therouting table 210 is referred by using the destination of this datagramto determine the output interface and the next hop network layer addressor output virtual connection identifier, and then this datagram is givento the datagram processing unit 22 of the output interface via thetransfer unit 30.

It is also to be noted here that in the first to third embodimentsdescribed above, a number of the virtual connection oriented LANs and/orthe non-virtual connection oriented LANs is arbitrary. In addition, thepresent invention may be applied to any type of LAN other than theATM-LAN and Ethernet used in the above description.

Referring now to FIG. 16 to FIG. 18, the fourth embodiment of a routerdevice according to the present invention will be described in detail.

This fourth embodiment concerns with a case of a router for connectingATM networks, which is capable of determining the output interface andvirtual connection identifier by using the input virtual connectionidentifier (VPI/VCI) without looking into the network layer datagram,and transferring the datagram as the AAL (ATM Adaptation Layer) frame(AAL PDU or AAL SDU).

In this fourth embodiment, the router device has a configuration asshown in FIG. 16, where a plurality of ATM NICs (Network InterfaceCards) 1000 and a CPU board 1100 for carrying out the network layerprocessing are connected to a single general purpose bus 1021. Inaddition, the general purpose bus 1021 may also be connected with anon-virtual connection oriented NIC such as an Ethernet NIC 2000. Notethat the general purpose bus 1021 may be replaced by a switch, ifdesired.

The CPU board 1100 carries out the network layer protocol processing bymeans of software processing, and includes a network layer protocolselection unit 1101 and a network layer protocol multiplexing unit 1102each of which is connected with the general purpose bus 1021, an IPprocessing unit 1103 and an IPX processing unit 1104 each of which isconnected with both the network layer protocol selection unit 1101 andthe network layer protocol multiplexing unit 1102, and a connectionidentifier analysis unit 1105. Here, the connection identifier analysisunit 1105 has a connection management table for registering inputVPI/VCI, output I/F, and output VPI/VCI or next hop network layeraddress in correspondence to input I/F as shown in FIG. 16.

The ATM NIC 1000 carries out the disassembly of the AAL frame into theATM cells and the assembly of the AAL frame from the ATM cells, andincludes an ATM reception unit 1001 connected with the ATM network 1023or 1025, an AAL reception processing unit 1002 connected with the ATMreception unit 1001, a reception buffer 1003 connected with the AALreception processing unit 1002, a bus transmission unit 1004 connectedwith the reception buffer 1003 and the general purpose bus 1021, a busreception unit 1005 connected with the general purpose bus 1021, atransmission buffer 1006 connected with the bus reception unit 1005, anAAL transmission processing unit 1007 connected with the transmissionbuffer 1006, and an ATM transmission unit 1008 connected with the AALtransmission processing unit 1007 and the ATM network 1023 or 1025.

The Ethernet NIC 2000 includes an Ethernet reception unit 2001 connectedwith the Ethernet, a reception buffer 2002 connected with the Ethernetreception unit 2001, a bus transmission unit 2003 connected with thereception buffer 2002 and the general purpose bus 1021, a bus receptionunit 2004 connected with the general purpose bus 1021, a transmissionbuffer 2005 connected with the bus reception unit 2004, and an Ethernettransmission unit 2006 connected with the transmission buffer 2005 andthe Ethernet.

As for a transfer scheme between one ATM NIC and another ATM ornon-virtual connection oriented NIC or CPU board, the following twoschemes are available.

The first scheme presents the reception buffer 1003 and the transmissionbuffer 1006 of the ATM NIC 1000 as shared memories to the CPU such thatthey appear similarly as a memory possessed by the CPU. By means ofthis, the reading and writing between the ATM NIC 1000 and the CPU board1100 can be realized by the CPU. The transfer between the ATM NICs canbe realized as the CPU reads from one ATM NIC 1000 and writes intoanother ATM NIC 1000. The transfer between the ATM NIC and the EthernetNIC can be realized similarly by replacing one ATM NIC 1000 in the abovecase with the Ethernet NIC 2000.

The second scheme realizes the data transfer in a form of reading fromthe ATM NIC 1000 to the CPU board 1100, or another ATM NIC 1000, or theEthernet NIC 2000, by specifying a transfer target memory address, adata size, and an address of the reception buffer 1003 of the ATM NIC1000, to the bus transmission unit 1004. In a case of writing into theATM NIC 1000, the data are transferred to the transmission buffer 1006by writing a transfer data size, a transmission source memory address,and a memory address of the transmission buffer 1006 of the transfertarget ATM NIC 1000 in the bus transmission unit 1004. Also, byreplacing the transfer target ATM NIC 1000 with the Ethernet NIC 2000,the transfer between the ATM NIC and the Ethernet NIC can be realizedsimilarly.

In the following, a procedure for transferring cells received from theATM network, either by carrying out the network layer processing or bykeeping a form of the AAL frame, will be described.

In the ATM NIC 1000, the ATM cells are received from the ATM network atthe ATM reception unit 1001, the received ATM cells are assembled intothe AAL frame at the AAL reception processing unit 1002, and theobtained AAL PDU and the VPI/VCI of a connection through which the ATMcells are received are stored into the reception buffer 1003. When dataare entered into the reception buffer 1003, the fact that data arereceived and the input interface are notified from the bus transmissionunit 1004 to the CPU board 1100.

In the CPU board 1100, after the data reception is recognized, the inputVPI/VCI is read out. Here, the input VPI/VCI may be notified from theATM NIC 1000 to the CPU board 1100 at a time of notifying the datareception. Then, the connection identifier analysis unit 1105 in the CPUboard 1100 determines the output interface and VPI/VCI or next hopnetwork layer address from the input interface and VPI/VCI.

The processing from here on is different for a case of carrying out thenetwork layer processing and a case of keeping a form of AAL frame (AALtransfer), so that these two cases will be described separately.

(1) A case of carrying out the network layer processing

When the output interface is the CPU board 1100 at the connectionidentifier analysis unit 1105, the AAL frame is transferred from thereception buffer 1003 of the ATM NIC 1000 to the network layer protocolselection unit 1101.

The network layer protocol selection unit 1101 removes a header/trailerof the data in the AAL frame according to a protocol type field in theAAL frame to covert the data into the datagrams, and gives the obtaineddatagrams to the corresponding network layer processing units (such asthe IP processing unit 1103 and the IPX processing unit 1104). Thenetwork layer processing units then carry out the processings unique tothe respective network layers. For example, at the IP processing unit1103, the TTL field in the packet is reduced, and the router to be sentnext is selected from the destination address.

The datagrams processed by the network layer processing units are thengiven to the network layer protocol multiplexing unit 1102, at which aheader having a protocol type field for indicating the network layer isattached to each datagram, the output VPI/VCI is obtained from theaddress of the router selected above, and the datagram with the headerattached is converted into the AAL frame. This AAL frame is thentransferred to the transmission buffer 1006 of the output interface byspecifying the transfer target memory address. In addition, the outputVPI/VCI obtained above is additionally written into the transmissionbuffer 1006, and the AAL transmission processing unit 1007 disassemblesthe AAL frame in the transmission buffer 1006 into the ATM cells. Then,the ATM transmission unit 1008 outputs these ATM cells to the ATMnetwork by using the output VPI/VCI written in the transmission buffer1006.

In the above, the AAL frame to be outputted and the output VPI/VCI areseparately transferred to the output ATM NIC, but it is also possible totransfer the AAL frame and the output VPI/VCI simultaneously.

When the output interface is the Ethernet NIC 2000, the AAL frameobtained by converting the datagrams processed at the network layerprocessing units is transferred to the transmisiosn buffer 2005. Then,at a time of conversion to the AAL frame, the Ethernet address isdetermined from the address (next hop network layer address) of theselected router, and this Ethernet address is additionally written intothe transmission buffer 2005. Then, this Ethernet address is attached tothe AAL frame in the transmission buffer 2005, and this AAL frame istransmitted from the Ethernet transmission unit 2006.

(2) A case of AAL transfer

When the output interface is other than the CPU board 1100 at theconnection identifier analysis unit 1105, the output interface and theposition of the transmission buffer 1006 of the output interface arespecified in order to send the AAL frame through the general purpose busto the output interface written in the connection management table. TheAAL frame is transferred from one ATM NIC to another ATM NIC by one ofthe two schemes described above, and stored in the transmission buffer1006 of the transmission interface. At this point, the connectionidentifier analysis unit 1105 enters the VPI/VCI to be used fortransmission in the transmission buffer 1006. Then, the AAL transmissionprocessing unit 1007 converts the AAL frame into the ATM cells, and theATM transmission unit 1008 outputs the ATM cells to the ATM network byusing the VPI/VCI written in the transmission buffer 1006.

In the above, the AAL frame to be outputted and the output VPI/VCI areseparately transferred to the output ATM NIC, but it is also possiblefor the connection identifier analysis unit 1105 to convert the inputVPI/VCI of the reception buffer 1003 into the output VPI/VCI, andtransfer the AAL frame and the output VPI/VCI simultaneously to thetransmission buffer.

When the output interface is the Ethernet NIC 2000, the following twoAAL transfer schemes are available.

In the first scheme, the AAL frame is transferred from the ATM NIC whichreceived the ATM cells to the Ethernet NIC of the output interfacewritten in the connection management table, while the connectionidentifier analysis unit 1105 enters the next hop network layer addresswritten in the connection management table into the transmission buffer2005, similarly as in the above described case in which the outputinterface is the ATM NIC. In this case, the Ethernet transmission unit2006 has an additional function for determining the Ethernet addressfrom the next hop network layer address, so that the correspondingEthernet address is obtained from the next hop network layer addressentered into the transmission buffer 2005, this Ethernet address isattached to the AAL frame in the transmission buffer 2005, and this AALframe is transmitted to the network.

In the second scheme, only the function for determining the Ethernetaddress from the next hop network layer address is utilized among thefunctions provided in the network layer protocol multplexing unit 1102as described for the above described case of carrying out the networklayer processing. In this case, the AAL frame is transferred from theATM NIC which received the ATM cells, while the Ethernet addresscorresponding to the next hop network layer address written in theconnection management table is obtained, and this Ethernet address iswritten into the transmission buffer 2005.

In this manner, by connecting a plurality of usual ATM NICs ornon-virtual connection oriented NICs to the general purpose bus, it ispossible to realize a high speed transfer by transferring the AAL frameas it is, without carrying out the network layer processing.

It is to be noted that the configuration of FIG. 16 can be modified asshown in FIG. 17, where each ATM NIC 1000 has a connection identifieranalysis unit 1009 connected between the reception buffer 1003 and thebus transmission unit 1004, instead of the connection identifieranalysis unit 1105 provided in the CPU board 1100 in the configurationof FIG. 16. This connection identifier analysis unit 1009 has a tableregistering output I/F and output VPI/VCI or next hop network layeraddress in correspondence to input VPI/VCI as shown in FIG. 17. Withthis modified configuration of FIG. 17, the additional mechanism isnecessary for the ATM NIC 1000, but the processing at the CPU board 1100can be reduced, so that the CPU processing load can be reduced. In thismodified configuration of FIG. 17, the operation is mostly similar tothat in the configuration of FIG. 16 described above.

It is also to be noted that the configuration of FIG. 16 may be expandedas shown in FIG. 18, where a plurality of general purpose buses 1029 and1031 and an internal bus 1027 are provided and connected through bridges1200, while the ATM NICs 1000 and the Ethernet NIC 2000 are connected tothe general purpose bus-2 1031, the CPU 1100 is connected to theinternal bus 1027, and a display card 1300 and other cards are connectedto the general purpose bus-1 1029, such that the display card 1300 andothers connected to the general purpose bus-1 1029 will not be affectedby the AAL frame transfer between the ATM NIC and another ATM NIC ornon-virtual connection oriented NIC. In this expanded configuration ofFIG. 18, the AAL frame to be transferred between the ATM NIC and anotherATM NIC or non-virtual connection oriented NIC will be transferred onlywithin the general purpose bus-2 1031, and not passed to the generalpurpose bus-1 1029 by means of the bridge 1200, so that it ispossible-to reduce the influence due to the AAL transfer on elementssuch as the CPU 1100 and the display card 1300 which are connected tobuses other than the general purpose bus-2 1031.

As described, according to the present invention, it is possible toimprove the transfer efficiency of the router device by determining theinformation for the transfer control and/or priority control (thenetwork interface which is the transfer target of the datagram or AALframe, and/or the quality of service of the datagram) from the virtualconnection identifier of the entered datagram or the assembled AALframe, without looking into the datagram content.

In the router device of the first embodiment, the network interface thatis the transfer target of the datagram can be determined by referring toa table according to the identifier of the virtual connection from whichthe datagram is entered, without looking into the datagram content, andthe datagram can be transferred to the determined network interface.Here, the router device may include means for applying the network layerprocessing to the datagram according to the protocol of the network.

This means for applying the network layer processing to the datagram ispreferably provided for each network interface. This is because theentered datagrams can be distributed to the output interfaces at highspeed according to the identifiers of the virtual connections, and thenetwork layer processings can be applied in parallel at the outputinterfaces.

Also, in the router device of the second embodiment, the quality ofservice of the datagram can be determined by referring to a tableaccording to the identifier of the virtual connection from which thedatagram is entered, without looking into the datagram content, and thepriority control for the datagrams can be carried out according to thedetermined quality of service.

Also, in the router device of the third embodiment, the networkinterface that is the transfer target of the datagram and the quality ofservice of the datagram can be determined by referring to a tableaccording to the identifier of the virtual connection from which thedatagram is entered, without looking into the datagram content, and thedatagram can be transferred to the determined network interface whilecarrying out the priority control for the datagrams according to thedetermined quality of service.

By obtaining the information from the virtual connection identifierbefore referring to the datagram itself in this manner, the workrequired for the router device can be reduced and the transferefficiency of the router device can be improved.

Note that the priority control may be carried out at a stage immediatelybefore the network layer processing according to the protocol of thenetwork is applied, or at a stage immediately before the datagram isoutputted to the output side network interface. It is also possible tocarry out the priority control at a stage immediately before thedatagram analysis to determine the transfer target network interfacefrom the datagram content.

Also, in the router device of the fourth embodiment, the networkinterface that is the transfer target of the AAL frame and the outputvirtual connection identifier can be determined by referring to a tableaccording to the identifier of the virtual connection from which the AALframe is entered, without assembling the datagram from the AAL framethat is assembled at the reception unit and looking into the datagramcontent, and the AAL frame can be transmitted to the virtual connectionhaving the determined output virtual connection identifier by thetransmission unit of the determined network interface. Here, thenotification of the determined output virtual connection identifier tothe transmission unit and the transfer of the AAL frame to thetransmission unit can be done in any desired order.

In this router device of the fourth embodiment, by obtaining theinformation from the virtual connection identifier without referring tothe datagram itself, the transfer efficiency of the router device can beimproved. In addition, because of the use of the AAL frame assembling,it is possible to prevent a transfer of those ATM cells which cannot beassembled into the AAL frame because of cell loss or some other causes,so that the utilization efficiency of the transmission channel can beincreased.

Also, when AAL5 is used, if the ATM cells received from a plurality ofinput connections are merged and transmitted to the output connection,it is impossible to assemble the AAL frame at the final destination in acase of the ATM cell transfer. However, by using the AAL transfer, theAAL frames received from a plurality of input connections can be mergedand transmitted to the output connection, so that it becomes easier todeal with the multicast.

Note that the transmission unit and the reception unit in this fourthembodiment can be provided in forms of network interface cards.

It is to be noted that, in the fourth embodiment described above, theconnection management table of the connection identifier analysis unitis used for determining an output interface to which the datagram is tobe transferred, but it is also possible to use the connection managementtable of the connection identifier analysis unit for determining anoutput virtual connection identifier corresponding to an inputconnection identifier, and transfer the datagram such that the datagramis outputted to a virtual connection having a virtual connectionidentifier identical to the determined output virtual connectionidentifier, in the similar manner as described above.

It is also to be noted that, besides those already mentioned above, manymodifications and variations of the above embodiments may be madewithout departing from the novel and advantageous features of thepresent invention. Accordingly, all such modifications and variationsare intended to be included within the scope of the appended claims.

1. A router device for transferring datagrams among networks comprising:network interfaces connected with networks including at least onevirtual connection oriented network; a memory for storing acorrespondence between a virtual connection identifier and a transfertarget network interface; connection identifier analysis means fordetermining a transfer target network interface for a datagram enteredfrom a virtual connection, by referring to the memory according to avirtual connection identifier of the virtual connection; and transfermeans for transferring the datagram to the transfer target networkinterface determined by the connection identifier analysis means.
 2. Therouter device of claim 1, further comprising reception means forreceiving a datalink frame from the virtual connection and assemblingthe datalink frame into the datagram.
 3. The router device of claim 1,wherein the memory also stores a correspondence between a virtualconnection identifier and an output virtual connection identifier to beused in a case where a network connected with the transfer targetnetwork interface is a virtual connection oriented network.
 4. Therouter device of claim 3, wherein the connection identifier analysismeans also notifies an output virtual connection identifier for thedatagram to the transfer target network interface.
 5. The A routerdevice of claim 1 for transferring datagrams among networks comprising:network interfaces connected with networks including at least onevirtual connection oriented network; a memory configured to store acorrespondence between a virtual connection identifier and a transfertarget network interface; a connection identifier analysis unitconfigured to determine a transfer target network interface for adatagram entered from a virtual connection, by referring to the memoryaccording to a virtual connection identifier of the virtual connection;and a transfer unit configured to transfer the datagram to the transfertarget network interface determined by the connection identifieranalysis unit, wherein the memory also stores a correspondence between athe virtual connection identifier and a next hop network layer addressto be used in a case where network connected with the transfer targetnetwork interface is a non-virtual connection oriented network.
 6. Therouter device of claim 5, wherein the connection identifier analysismeans unit also notifies a next hop network layer address for thedatagram to the transfer target network interface.
 7. The A routerdevice of claim 1, further comprising: for transferring datagrams amongnetworks comprising: network interfaces connected with networksincluding at least one virtual connection oriented network; a memoryconfigured to store a correspondence between a virtual connectionidentifier and a transfer target network interface; a connectionidentifier analysis unit configured to determine a transfer targetnetwork interface for a datagram entered from a virtual connection, byreferring to the memory according to a virtual connection identifier ofthe virtual connection; a transfer unit configured to transfer thedatagram to the transfer target network interface determined by theconnection identifier analysis unit; and a datagram analysis means forregisteringunit configured to register in advance a correspondencebetween a datagram content and a transfer target network interface, anddeterminingto determine a transfer target network interface for thedatagram according to a datagram content of the datagram when the memorydoes not store the transfer target network interface in correspondenceto the virtual connection identifier of the virtual connection; ,wherein the transfer means unit transfers the datagram to the transfertarget network interface determined by the datagram analysis means unitwhen the memory does not store the transfer target network interface incorrespondence to the virtual connection identifier of the virtualconnection.
 8. The A router device of claim 1 for transferring datagramsamong networks comprising: network interfaces connected with networksincluding at least one virtual connection oriented network; a memoryconfigured to store a correspondence between a virtual connectionidentifier and a transfer target network interface; a connectionidentifier analysis unit configured to determine a transfer targetnetwork interface for a datagram entered from a virtual connection, byreferring to the memory according to a virtual connection identifier ofthe virtual connection; and a transfer unit configured to transfer thedatagram to the transfer target network interface determined by theconnection identifier analysis unit, wherein: the memory also stores acorrespondence between a virtual connection identifier and a quality ofservice; the connection identifier analysis means unit also determines aquality of service for the datagram by referring to the memory accordingto a virtual connection identifier of the virtual connection; and therouter device further comprises: a scheduler means forapplyingconfigured to apply a priority control for datagrams to betransferred by the router device according to the quality of servicedetermined by the connection identifier analysis meansunit, such thatthe transfer meansunit transfers the datagram to which the prioritycontrol is applied by the scheduler means .
 9. The router device ofclaim 8, further comprising: a datagram analysis means forregisteringunit configured to register in advance a correspondencebetween a datagram content and a transfer target network interface, anddeterminingto determine a transfer target network interface for thedatagram to which the priority control is applied by the scheduler meansaccording to a datagram content of the datagram; wherein the schedulermeans makes the priority control of orders in which datagrams are givento the datagram analysis means unit.
 10. The router device of claim 8,further comprising: processing means for determininga processorconfigured to determine a transfer target network interface and/or nexthop network layer address and to applyingapply a network layerprocessing for the datagram to be transferred by the router device;,wherein the scheduler means makes the priority control of orders inwhich datagrams are given to the processing means processor.
 11. Therouter device of claim 1, further comprising datagram processing meansfor applying a network layer processing to the datagram to betransferred by the router device.
 12. The A router device of claim 11for transferring datagrams among networks comprising: network interfacesconnected with networks including at least one virtual connectionoriented network; a memory configured to store a correspondence betweena virtual connection identifier and a transfer target network interface;a connection identifier analysis unit configured to determine a transfertarget network interface for a datagram entered from a virtualconnection, by referring to the memory according to a virtual connectionidentifier of the virtual connection; and a transfer unit configured totransfer the datagram to the transfer target network interfacedetermined by the connection identifier analysis unit; and a datagramprocessing unit configured to apply network layer processing to thedatagram to be transferred by the router device, wherein the datagramprocessing meansunit is separately provided for each network interface.13. A router device for transferring datagrams among networks,comprising: at least one network interface connected with at least onevirtual connection oriented network; a memory for storing acorrespondence between a virtual connection identifier and an outputvirtual connection identifier; connection identifier analysis means fordetermining an output virtual connection identifier for a datagramentered from a virtual connection, by referring to the memory accordingto a virtual connection identifier of the virtual connection; andtransfer means for transferring the datagram such that the datagram isoutputted to a virtual connection having the output virtual connectionidentifier determined by the connection identifier analysis means. 14.The router device of claim 13, further comprising reception means forreceiving a datalink frame from the virtual connection and assemblingthe datalink frame into the datagram.
 15. A router device fortransferring datagrams among networks, comprising: at least one networkinterface connected with at least one virtual connection orientednetwork; a memory for storing configured to store a correspondencebetween a virtual connection identifier and a quality of service; aconnection identifier analysis means for determiningunit configured todetermine a quality of service for a datagram entered from a virtualconnection, by referring to the memory according to a virtual connectionidentifier of the virtual connection; a scheduler means forapplyingconfigured to apply a priority control for datagrams to betransferred by the router device according to the quality of servicedetermined by the connection identifier analysis meansunit; and atransfer means for transferringunit configured to transfer the datagramto which the priority control is applied by the scheduler means . 16.The router device of claim 15, further comprising: a datagram analysismeans for registeringunit configured to register in advance acorrespondence between a datagram content and a transfer target networkinterface, and determiningto determine a transfer target networkinterface for the datagram to which the priority control is applied bythe scheduler means according to a datagram content of the datagram; ,wherein the scheduler means makes the priority control of orders inwhich datagrams are given to the datagram analysis means unit.
 17. Therouter device of claim 15, further comprising: processing means fordetermininga processor configured to determine a transfer target networkinterface and/or next hop network layer address and to applying anetwork layer processing for the datagram to be transferred by therouter device; , wherein the scheduler means makes the priority controlof orders in which datagrams are given to the processing meansprocessor.
 18. A router device for transferring AAL frames from an ATMnetwork through network interfaces connected with networks including atleast one ATM network, each network interface connected with said atleast one ATM network including reception means for receiving ATM cellsfrom an ATM network and assembling an AAL frame from the received ATMcells, and transmission means for forming ATM cells from an AAL frameand transmitting the formed ATM cells to an ATM network, the routerdevice comprising: a memory for storing a correspondence between avirtual connection identifier and a transfer target network interface;connection identifier analysis means for determining a transfer targetnetwork interface for an AAL frame assembled from ATM cells entered froma virtual connection, by referring to the memory according to a virtualconnection identifier of the virtual connection; processing means fordetermining a transfer target network interface for the AAL frame byassembling datagram from the AAL frame and analyzing the assembleddatagram, when the memory does not store the transfer target networkinterface in correspondence to the virtual connection identifier of thevirtual connection; and transfer means for transferring the AAL frame tothe transfer target network interface determined by one of theconnection identifier analysis means and the processing means.
 19. AnATM network interface card device for interfacing an ATM network and abus for connecting other network interfaces connected with othernetworks, the ATM network interface card device comprising: receptionmeans for receiving ATM cells from the ATM network and assembling an AALframe from the received ATM cells; a memory for storing a correspondencebetween a virtual connection identifier and a transfer target networkinterface; connection identifier analysis means for determining atransfer target network interface for an AAL frame assembled from ATMcells entered from a virtual connection, by referring to the memoryaccording to a virtual connection identifier of the virtual connection;and transfer means for transferring the AAL frame through the bus to thetransfer target network interface determined by the connectionidentifier analysis means.
 20. A router device for transferringdatagrams among networks, comprising: at least one network interfaceconnected with at least one virtual connection oriented network; amemory for storing configured to store a correspondence between avirtual connection identifier and a protocol type information indicatinga type and/or a version of a protocol; a connection identifier analysismeans for determiningunit configured to determine a protocol typeinformation for a datagram entered from a virtual connection, byreferring to the memory according to a virtual connection identifier ofthe virtual connection; a datagram analysis means for determiningunitconfigured to determine a transfer target network interface/next hopnetwork layer address for the datagram according to a datagram contentof the datagram, the datagram analysis meansunit having a plurality ofprocessors in correspondence to different protocols, and the datagram isentered into one of said plurality of processors which corresponds to aprotocol of a type and/or a version indicated by the protocol typeinformation determined by the connection identifier analysis meansunit;and a transfer means for transferringunit configured to determine thedatagram to the transfer target network interface/next hop network layeraddress determined by the datagram analysis meansunit.
 21. A method fortransferring datagrams among networks, using a router device havingnetwork interfaces connected with networks including at least onevirtual connection oriented network, the method comprising the steps of:storing a correspondence between a virtual connection identifier and atransfer target network interface in a memory provided at the routerdevice; determining a transfer target network interface for a datagramentered from a virtual connection at the router device, by referring tothe memory according to a virtual connection identifier of the virtualconnection; and transferring the datagram to the transfer target networkinterface determined by the determining step.
 22. A method fortransferring datagrams among networks, using a router device having atleast one network interface connected with at least one virtualconnection oriented network, the method comprising the steps of: storinga correspondence between a virtual connection identifier and an outputvirtual connection identifier in a memory provided at the router device;determining an output virtual connection identifier for a datagramentered from a virtual connection, by referring to the memory accordingto a virtual connection identifier of the virtual connection; andtransferring the datagram such that the datagram is outputted to avirtual connection having the output virtual connection identifierdetermined by the determining step.
 23. A method for transferringdatagrams among networks, using a router device having at least onenetwork interface connected with at least one virtual connectionoriented network, the method comprising the steps of: storing acorrespondence between a virtual connection identifier and a quality ofservice in a memory provided at the router device; determining a qualityof service for a datagram entered from a virtual connection at therouter device, by referring to the memory according to a virtualconnection identifier of the virtual connection; applying a prioritycontrol for datagrams to be transferred by the router device accordingto the quality of service determined by the determining step; andtransferring the datagram to which the priority control is applied bythe applying step.
 24. A method for transferring AAL frames from an ATMnetwork, using a router device having network interfaces connected withnetworks including at least one ATM network, each network interfaceconnected with said at least one ATM network including reception meansfor receiving ATM cells from an ATM network and assembling an AAL framefrom the received ATM cells, and transmission means for forming ATMcells from an AAL frame and transmitting the formed ATM cells to an ATMnetwork, the method comprising the steps of: storing a correspondencebetween a virtual connection identifier and a transfer target networkinterface in a memory provided at the router device; determining atransfer target network interface for an AAL frame assembled from ATMcells entered from a virtual connection, by referring to the memoryaccording to a virtual connection identifier of the virtual connection;processing the AAL frame to determine a transfer target networkinterface for the AAL frame by assembling datagram from the AAL frameand analyzing the assembled datagram, when the memory does not store thetransfer target network interface in correspondence to the virtualconnection identifier of the virtual connection; and transferring theAAL frame to the transfer target network interface determined by one ofthe determining step and the processing step.
 25. A method forinterfacing an ATM network and a bus for connecting other networkinterfaces connected with other networks, the method comprising thesteps of: receiving ATM cells from the ATM network and assembling an AALframe from the received ATM cells; storing a correspondence between avirtual connection identifier and a transfer target network interface ina memory; determining a transfer target network interface for an AALframe assembled from ATM cells entered from a virtual connection, byreferring to the memory according to a virtual connection identifier ofthe virtual connection; and transferring the AAL frame through the busto the transfer target network interface determined by the determiningstep.
 26. A method for transferring datagrams among networks, using arouter device having at least one network interface connected with atleast one virtual connection oriented network, the method comprising thesteps of: storing a correspondence between a virtual connectionidentifier and a protocol type information indicating a type and/or aversion of a protocol in a memory provided at the router device;determining a protocol type information for a datagram entered from avirtual connection, by referring to the memory according to a virtualconnection identifier of the virtual connection; determining a transfertarget network interface/next hop network layer address for the datagramaccording to a datagram content of the datagram, wherein a plurality ofprocessors are provided at the router device in correspondence todifferent protocols, and the datagram is entered into one of saidplurality of processors which corresponds to a protocol of a type and/ora version indicated by the protocol type information determined by thedetermining step; and transferring the datagram to the determinedtransfer target network interface/next hop network layer address.
 27. Adata communication network system, comprising: networks including atleast one virtual connection oriented network; a transmission nodeprovided in each network for transmitting datagrams such that datagramsdestined to an identical destination are transmitted through at leastone specific virtual connection; and a router device for connecting atleast two of the networks, the router device including: networkinterfaces connected with said at least two of the networks; a memoryfor storing a correspondence between a virtual connection identifier anda transfer target network interface; connection identifier analysismeans for determining a transfer target network interface for a datagramentered from a virtual connection, by referring to the memory accordingto a virtual connection identifier of the virtual connection; andtransfer means for transferring the datagram to the transfer targetnetwork interface determined by the connection identifier analysismeans.
 28. A data communication network system, comprising: networksincluding at least one virtual connection oriented network; atransmission node provided in each network for transmitting datagramssuch that datagrams destined to an identical destination are transmittedthrough at least one specific virtual connection; and a router devicefor connecting at least two of the networks, the router deviceincluding: at least one network interface connected with said at leasttwo of the networks; a memory for storing a correspondence between avirtual connection identifier and an output virtual connectionidentifier; connection identifier analysis means for determining anoutput virtual connection identifier for a datagram entered from avirtual connection, by referring to the memory according to a virtualconnection identifier of the virtual connection; and transfer means fortransferring the datagram such that the datagram is outputted to avirtual connection having the output virtual connection identifierdetermined by the connection identifier analysis means.
 29. A datacommunication network system, comprising: networks including at leastone virtual connection oriented network; a transmission node provided ineach network for transmitting configured to transmit datagrams such thatdatagrams with an identical quality of service are transmitted throughat least one specific virtual connection; and a router device forconnecting configured to connect at least two of the networks, therouter device including: , at least one network interface connected withsaid at least two of the networks; , a memory for storing configured tostore a correspondence between a virtual connection identifier and aquality of service; , a connection identifier analysis unit means fordeterminingconfigured to determine a quality of service for a datagramentered from a virtual connection, by referring to the memory accordingto a virtual connection identifier of the virtual connection;, ascheduler means for applyingconfigured to apply a priority control fordatagrams to be transferred by the router device according to thequality of service determined by the connection identifier analysismeans;, and a transfer means for transferringunit configured to transferthe datagram to which the priority control is applied by theschedulermeans .
 30. A data communication network system, comprising:networks including at least one ATM network; a transmission nodeprovided in each network for transmitting datagrams such that datagramsdestined to an identical destination are transmitted through at leastone specific virtual connection; and a router device for connecting atleast two of the networks, and for transferring AAL frames from an ATMnetwork through network interfaces connected with the networks, eachnetwork interface connected with said at least one ATM network includingreception means for receiving ATM cells from an ATM network andassembling an AAL frame from the received ATM cells, and transmissionmeans for forming ATM cells from an AAL frame and transmitting theformed ATM cells to an ATM network, the router device including: amemory for storing a correspondence between a virtual connectionidentifier and a transfer target network interface; connectionidentifier analysis means for determining a transfer target networkinterface for an AAL frame assembled from ATM cells entered from avirtual connection, by referring to the memory according to a virtualconnection identifier of the virtual connection; processing means fordetermining a transfer target network interface for the AAL frame byassembling datagram from the AAL frame and analyzing the assembleddatagram, when the memory does not store the transfer target networkinterface in correspondence to the virtual connection identifier of thevirtual connection; and transfer means for transferring the AAL frame tothe transfer target network interface determined by one of theconnection identifier analysis means and the processing means.
 31. Adata communication network system, comprising: networks including atleast one ATM network; a transmission node provided in each network fortransmitting datagrams such that datagrams destined to an identicaldestination are transmitted through at least one specific virtualconnection; and a router device for connecting at least two of thenetworks including an ATM network; and an ATM network interface carddevice for interfacing an ATM network and a bus for connecting othernetwork interfaces connected with other networks, the ATM networkinterface card device including: reception means for receiving ATM cellsfrom the ATM network and assembling an AAL frame from the received ATMcells; a memory for storing a correspondence between a virtualconnection identifier and a transfer target network interface;connection identifier analysis means for determining a transfer targetnetwork interface for a AAL frame assembled from ATM cells entered froma virtual connection, by referring to the memory according to a virtualconnection identifier of the virtual connection; and transfer means fortransferring the AAL frame through the bus to the transfer targetnetwork interface determined by the connection identifier analysismeans.
 32. A data communication network system, comprising: networksincluding at least one virtual connection oriented network; atransmission node provided in each network for transmitting configuredto transmit datagrams such that datagrams of an identical protocol typeand/or version are transmitted through at least one specific virtualconnection; and a router device for connecting configured to connect atleast two of the networks, the router device including: , at least onenetwork interface connected with said at least two of the networks; , amemory for storing configured to store a correspondence between avirtual connection identifier and a protocol type information indicatinga type and/or a version of a protocol; , a connection identifieranalysis means for determiningunit configured to determine a protocoltype information for a datagram entered from a virtual connection, byreferring to the memory according to a virtual connection identifier ofthe virtual connection; , a datagram analysis unit means fordeterminingconfigured to determine a transfer target networkinterface/next hop network layer address for the datagram according to adatagram content of the datagram, the datagram analysis meansunit havinga plurality of processors in correspondence to different protocols, andthe datagram is entered into one of said plurality of processors whichcorresponds to a protocol of a type and/or a version indicated by theprotocol type information determined by the connection identifieranalysis means;unit, and a transfer means for transferringunitconfigured to transfer the datagram to the transfer target networkinterface/next hop network layer address determined by the datagramanalysis meansunit.
 33. A transmission node device for transmittingdatagrams to a router device, comprising: a memory for storing acorrespondence between a destination and an output virtual connectionidentifier, the correspondence being known to the router device;datagram analysis means for determining an output virtual connectionidentifier for a datagram to be transmitted, by referring to the memoryaccording to a destination of the datagram; and transmission means fortransmitting the datagram to a virtual connection having the outputvirtual connection identifier determined by the datagram analysis means,such that datagrams destined to an identical destination are transmittedthrough at least one specific virtual connection.
 34. A transmissionnode device for transmitting datagrams to a router device, comprising: amemory for storing configured to store a correspondence between aquality of service specifying information indicating a quality ofservice and an output virtual connection identifier, the correspondencebeing known to the router device; a datagram analysis means fordeterminingunit configured to determine an output virtual connectionidentifier for a datagram to be transmitted, by referring to the memoryaccording to a quality of service specifying information of thedatagram; and a transmission means for transmittingunit configured totransfer the datagram to a virtual connection having a virtualconnection identifier identical to the output virtual connectionidentifier determined by the datagram analysis meansunit, such thatdatagrams with an identical quality of service specifying informationare transmitted through at least one specific virtual connection.
 35. Atransmission node device for transmitting datagrams to a router device,comprising: a memory for storing configured to store a correspondencebetween a protocol type information indicating a type and/or a versionof a protocol and an output virtual connection identifier, thecorrespondence being known to the router device; a datagram analysismeans for determiningunit configured to determine an output virtualconnection identifier for a datagram to be transmitted, by referring tothe memory according to a type and/or a version of a protocol of thedatagram; and a transmission means for transmittingunit configured totransmit the datagram to a virtual connection having a virtualconnection identifier identical to the output virtual connectionidentifier determined by the datagram analysis meansunit, such thatdatagrams of an identical protocol type and/or version are transmittedthrough at least one specific virtual connection.
 36. A method fortransmitting datagrams to a router device, comprising the steps of:storing in a memory a correspondence between a destination and an outputvirtual connection identifier, the correspondence being known to therouter device; determining an output virtual connection identifier for adatagram to be transmitted, by referring to the memory according to adestination of the datagram; and transmitting the datagram to a virtualconnection having the output virtual connection identifier determined bythe determining step, such that datagrams destined to an identicaldestination are transmitted through at least one specific virtualconnection.
 37. A method for transmitting datagrams to a router device,comprising the steps of: storing in a memory a correspondence between aquality of service specifying information indicating a quality ofservice and an output virtual connection identifier, the correspondencebeing known to the router device; determining an output virtualconnection identifier for a datagram to be transmitted, by referring tothe memory according to a quality of service specifying information ofthe datagram; and transmitting the datagram to a virtual connectionhaving a virtual connection identifier identical to the output virtualconnection identifier determined by the determining step, such thatdatagrams with an identical quality of service specifying informationare transmitted through at least one specific virtual connection.
 38. Amethod for transmitting datagrams to a router device, comprising thesteps of: storing in a memory a correspondence between a protocol typeinformation indicating a type and/or a version of a protocol and anoutput virtual connection identifier, the correspondence being known tothe router device; determining an output virtual connection identifierfor a datagram to be transmitted, by referring to the memory accordingto a type and/or a version of a protocol of the datagram; andtransmitting the datagram to a virtual connection having a virtualconnection identifier identical to the output virtual connectionidentifier determined by the determining step, such that datagrams of anidentical protocol type and/or version are transmitted through at leastone specific virtual connection.
 39. A router device for transferringdatagrams among networks comprising: network interfaces connected withnetworks including at least one virtual connection oriented network andat least one non-virtual connection oriented network; a memoryconfigured to store a correspondence between a virtual connectionidentifier and a transfer target network interface, and also to store acorrespondence between the virtual connection identifier and a networklayer address; a first connection identifier analysis unit configured todetermine a transfer target network interface for a datagram enteredfrom a virtual connection, by referring to the memory according to avirtual connection identifier of the virtual connection; a secondconnection identifier analysis unit configured to determine a transfertarget network layer address for the datagram entered from the virtualconnection, by referring to the memory according to the virtualconnection identifier of the virtual connection; a first transfer unitconfigured to transfer the datagram to the transfer target networkinterface connected with another virtual connection oriented network,when the transfer target network interface is determined by the firstconnection identifier analysis unit; and a second transfer unitconfigured to transfer the datagram to the transfer target networkinterface connected with the at least one non-virtual connectionoriented network toward the transfer target network layer address, whenthe transfer target network layer address is determined by the secondconnection identifier analysis unit.
 40. A router device according toclaim 39, wherein: the transfer target network interface is configuredto transfer the datagrams toward a datalink address determined using thetransfer target network layer address.
 41. A router device according toclaim 39, wherein: a transfer target of the datagram is determinedwithout referring to the datagram content.
 42. A method for transferringdatagrams among networks, using a router device having networkinterfaces connected with networks including at least one virtualconnection oriented network and at least one non-virtual connectionoriented network, the method comprising the steps of: storing acorrespondence between a virtual connection identifier and a transfertarget network interface in a memory provided at the router device, andalso storing a correspondence between the virtual connection identifierand a network layer address first determining a transfer target networkinterface for a datagram entered from a virtual connection at the routerdevice, by referring to the memory according to a virtual connectionidentifier of the virtual connection; second determining a transfertarget network layer address for the datagram entered from the virtualconnection, by referring to the memory according to the virtualconnection identifier of the virtual connection; first transferring thedatagram to the transfer target network interface connected with anothervirtual connection oriented network, when the transfer target networkinterface is determined by the first determining step; and secondtransferring the datagram to the transfer target network interfaceconnected with the at least one non-virtual connection oriented networktoward the transfer target network layer address, when the transfertarget network layer address is determined by the second determiningstep.
 43. A method according to claim 42, wherein: the step of secondtransferring transmits the datagrams from the transfer target networkinterface toward a datalink address determined using the transfer targetnetwork layer address.
 44. A method according to claim 42, wherein: thestep of determining the transfer target network layer address isperformed without referring to the datagram content.
 45. A method fortransferring datagrams among networks, using at least two router deviceshaving network interfaces connected with networks including at least onevirtual connection oriented network, the method comprising the steps of:storing a correspondence between a virtual connection identifier and atransfer target network interface in a memory provided at a routerdevice; determining transfer target network interface for a datagramentered from a virtual connection at the router device, by referring tothe memory according to a virtual connection identifier of the virtualconnection on which the datagram is received; transferring the datagramto the transfer target network interface determined by the determiningstep; first transmitting the datagram along with another virtualconnection identifier from the transfer target network interface over asecond virtual connection to another router device; receiving thedatagram, at said another router device, from the transfer targetnetwork interface at the router device over the second virtualconnection; removing said another virtual connection identifier from thedatagram at said another router device; and second transmitting saiddatagram, at said another router device, away from said another routerdevice without said another virtual connection identifier, and withoutadding another virtual connection identifier.
 46. A method according toclaim 45, wherein said step of second transmitting said datagram awayfrom said another router device comprises transmitting said datagramover a non-virtual connection oriented network.
 47. A method accordingto claim 46, wherein said step of second transmitting said datagram wayfrom said another router device comprises transmitting said datagram toa location using a network layer address associated with the datagram.48. A method according to claim 45, wherein said step of secondtransmitting said datagram way from said another router device comprisestransmitting said datagram to a location using a network layer addressassociated with the datagram.
 49. A method according to claim 48,wherein said step of second transmitting said datagram way from saidanother router device comprises transmitting said datagram withoutreferring to the datagram content to a location using a network layeraddress associated with the datagram.
 50. A method for transferringdatagrams among networks, using a router device having networkinterfaces connected with networks including at least one virtualconnection oriented network, the method comprising the steps of: storinga correspondence between a virtual connection identifier and a transfertarget network interface in a memory provided at the router device;determining a transfer target network interface for a datagram enteredfrom a virtual connection at the router device, by referring to thememory according to a virtual connection identifier of the virtualconnection on which the datagram is received; transferring the datagramto the transfer target network interface determined by the determiningstep; and transmitting said datagram from the router device without saidvirtual connection identifier, and without adding another virtualconnection identifier.
 51. A plurality of router devices fortransferring datagrams among networks, comprising: a first router deviceincluding, a first set of network interfaces connected to at least afirst virtual connection oriented network, a first memory configured tostore a first correspondence between a first input virtual connectionidentifier and a first transfer target network interface, a firstconnection identifier analysis unit configured to determine the firsttransfer target network interface for a first datagram entered from afirst input virtual connection, by referring to the first memoryaccording to the first input virtual connection identifier of the firstvirtual connection, and a first transfer unit configured to transfer thefirst datagram to the first transfer target network interface determinedby the first connection identifier analysis unit; and a second routerdevice including, a second set of network interfaces connected to atleast a second virtual connection oriented network, a second memoryconfigured to store a second correspondence between a second inputvirtual connection identifier and a next hop layer address to be used ina case where the second set of network interfaces is connected to atleast a non-virtual connection oriented network, a second connectionidentifier analysis unit configured to determine a second transfertarget network interface for a second datagram entered from a secondinput virtual connection, by referring to the second memory according tothe second input virtual connection identifier of the second virtualconnection, and a second transfer unit configured to transfer the seconddatagram to the second transfer target network interface determined bythe second connection identifier analysis unit.
 52. A method fortransferring datagrams among networks, using a first router device and asecond router device having network interfaces connected with networksincluding at least one virtual connection oriented network, the methodcomprising the steps of: storing a correspondence between a firstvirtual connection identifier and a first transfer target networkinterface in a memory provided at the first router device; determining afirst transfer target network interface for a datagram entered from afirst virtual connection at the first router, by referring to the memoryprovided at the first router device according to a virtual connectionidentifier of the first virtual connection; transferring the datagramentered from the first virtual connection to the first transfer targetnetwork interface determined by the determining step; storing acorrespondence between a second virtual connection identifier and asecond transfer target network interface in a memory provided at thesecond router device, said second transfer target network interfacebeing connected to a next hop network layer address to be used in a casewhere the network interfaces of the second router is connected to atleast a non-virtual connection oriented network; determining a secondtransfer target network interface for a datagram entered from a secondvirtual connection at the second router, by referring to the memoryprovided at the second router device according to a virtual connectionidentifier of the second virtual connection; transferring the datagramentered at the second virtual connection to the second transfer targetnetwork interface determined by the determining step.
 53. A plurality ofrouter devices for transferring datagrams among networks, comprising: afirst router device including, a first set of network interfacesconnected to at least a first virtual connection oriented network, afirst memory configured to store a first correspondence between a firstinput virtual connection identifier and a first output virtualconnection identifier, a first connection identifier analysis unitconfigured to determine the first transfer target network interface fora first datagram entered from a first input virtual connection, byreferring to the first memory according to the first input virtualconnection identifier of the first virtual connection, and a firsttransfer unit configured to transfer the first datagram to the firsttransfer target network interface determined by the first connectionidentifier analysis unit a second router device including, a second setof network interfaces connected to at least a second virtual connectionoriented network, a second memory configured to store a secondcorrespondence between a second input virtual connection identifier, asecond transfer target network interface, and a second output virtualconnection identifier, a second connection identifier analysis unitconfigured to determine the second transfer target network interface fora second datagram entered from a second input virtual connection, byreferring to the second memory according to the second input virtualconnection identifier of the second virtual connection, and a secondtransfer unit configured to transfer the second datagram to the secondtransfer target network interface determined by the second connectionidentifier analysis unit without attaching said second output virtualconnection identifier to said second datagram.
 54. A method fortransferring datagrams among networks, using a first router device and asecond router device having network interfaces connected with networksincluding at least one virtual connection oriented network, the methodcomprising the steps of: storing a correspondence between a firstvirtual connection identifier and a first transfer target networkinterface in a memory provided at the first router device; determining afirst transfer target network interface for a datagram entered from afirst virtual connection at the first router, by referring to the memoryprovided at the first router device according to a virtual connectionidentifier of the first virtual connection; transferring the datagramentered from the first virtual connection to the first transfer targetnetwork interface determined by the determining step; storing acorrespondence between a second virtual connection identifier and asecond transfer target network interface in a memory provided at thesecond router device; determining a second transfer target networkinterface for a datagram entered from a second virtual connection at thesecond router, by referring to the memory provided at the second routerdevice according to a virtual connection identifier of the secondvirtual connection; and transferring the datagram entered at the secondvirtual connection to the second transfer target network interfacedetermined by the determining step without attaching an output virtualconnection identifier to said datagram entered from the second virtualconnection.